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EQUINE   ANATOMY 


AND 


PHYSIOLOGY 


BALLOU 


BLAKISTON'S     ?  Q  U  IZ-COMP  E  N  PS  ? 

A   COJWPEND 

OF 

EQUINE  ANATOMY 


AND 


PHYSIOLOGY 


BY    v^' 

WILLIAM  R.  BALLOU,  M.D.    ,eb4- 

FORMERLY    PROFESSOR    OF    EQUINE   ANATOMY   AND    LECTURER   ON    PHYSIOLOGY,    NEW 

YORK    COLLEGE  OF  VETERINARY  SURGEONS;    INSTRUCTOR  IN  GENITO-URINARY 

SURGERY,  NEW    YORK    POLYCLINIC;    SURGEON  BELLEVUE  DISPENSARY; 

LATE   HOUSE    SURGEON,    BELLEVUE   HOSPITAL,    NEW    YORK. 


WITH 

TWENTY-NINE  GRAPHIC  ILLUSTRATIONS 

SELECTED    FROM 

CHAUVEAU'S  "COMPARATIVE  ANATOMY." 


PHILADELPHIA 

P.  BLAKISTON'S   SON  SiCOy 

i o: 2  WALNUT  STREET,  } 
1907 


Copyright,  1890,  by  P.  Blakiston,  Son  &  Co. 


"  \    Pr\nt£cbby "     ,' 
,The  'Xfictpe;  Prh%' 
York',  Pa.     ' 


TO  MY    STUDENTS    AT   THE. 

NEW   YORK   COLLEGE   OF   VETERINARY   SURGEONS 

THIS  LITTLE   WORK   IS    DEDICATED, 

IN   THE   HOPE   THAT   IT   MAY   ASSIST   THEM 

DURING    THEIR   LIFE   WORK, 

WITH   THE    KINDEST    WISHES    OF 

THE    AUTHOR. 


85U2 


PREFACE. 


The  popularity  of  this  series  of  "  Compends"  demonstrates  that 
they  supply  a  long-felt  want.  From  a  considerable  experience  as 
a  quiz-master  of  medical  students  and  a  teacher  of  anatomy,  the 
writer  has  seen  the  benefits  of  these,  and  has  endeavored  to  sup- 
ply for  students  of  veterinary  anatomy  and  physiology  a  work 
which  would  answer  their  needs  not  only  as  a  text-book,  but  also 
for  work  in  the  dissecting-room. 

While,  in  the  main,  the  standard  work  of  Chauveau  has  been 
followed,  the  works  of  Strangeways,  Gray  and  Quain  have  been 
consulted.  In  the  section  on  Physiology  the  late  works  of  Flint, 
Meade,  Smith  and  Jeffrey  Bell  have  furnished  the  greater  part  of 
the  data,  and  to  them  indebtedness  is  due.  Many  of  the  chem- 
ical analyses  have  been  taken  from  Charles 

Lack  of  space  necessitated  a  condensation  of  some  subjects  to 
narrow  limits,  while  others  have  been  merely  alluded  to.  The 
author  trusts  it  will  meet  the  same  cordial  welcome  from  the  vet- 
erinary profession  which  the  other  works  of  this  series  have  re- 
ceived from  their  fellow-workers  in  medicine. 

My  acknowledgments  are  due  to  Messrs.  D.  Appleton  &  Co., 
the  publishers  of  Chauveau's  'l  Comparative  Anatomy  of  Domes- 
ticated Animals,"  for  their  courtesy  in  supplying  the  illustrations 
I  have  used. 

fix) 


CONTENTS 


PAGE 

Anatomy 9 

Physiology 9 

Anatomy,  Divisions  of 9 

Osteology 9 

Bones,  Varieties  9 

Structure  of 10 

Vertebral  Column 11 

Head 13 

Face 18 

Fossae  of  Skull 23 

Hyoid 24 

Bones  of  Thorax   24 

Anterior  Extremity 25 

Posterior  Extremity 31 

Arthrology 37 

Classes  of  Articulations 37 

Structure  of  Articulations 38 

Articulations  of  Vertebral  Column 38 

Lower  Jaw   39 

Hyoid 40 

Thorax 40 

Anterior  Limb    41 

Posterior  Limb 45 

Myology 50 

Structure  of  Muscles 50 

Varieties  of  Muscles 50 

Appendages  of  Muscles 50 

Muscles  of  Face 51 

Mastication  .  . . 53 

Hyoid 54 

Tongue 55 

Palate 55 

Pharynx 56 

Trunk 57 

Inferior  Cervical  Region 57 

Back 62 

Thorax 63 

Abdomen 65 

(xi) 


Xll  CONTENTS. 

Inguinal  Canal 66 

Muscles  of  Anterior  Extremity 66 

Pelvis 72 

Thigh :.:::::::::::::::  75 

Leg 77 

Tail 80 

Angeiology 81 

Pericardium 81 

Heart  [  .  ,  81 

Arteries  of  Anterior  Extremity 85 

Head  and  Neck 89 

Trunk 93 

Posterior  Extremity 96 

Artery,  Pulmonary 08 

Veins,  Structure  of 98 

Head  and  Neck 99 

Anterior  Extremity 99 

Abdomen  and  Pelvis 101 

Posterior  Extremity 102 

Pulmonary 102 

Lymphatics 102 

Neurology 103 

Nervous  System,  Structure  of 103 

Spinal  Cord 103 

Membranes  of 103 

Brain,  Membranes  of 105 

Medulla  Oblongata  105 

Pons  Varolii.  . 106 

Cerebellum 107 

Cerebrum 107 

Ventricles  of 109 

Nerves,  Cranial in 

Cervical 115 

Brachial  Plexus  of •. 115 

Lumbo-Sacral  Plexus  of 117 

Dorsal 118 

Sympathetic  Nervous  System 118 

Viscera 120 

Digestive  System 120 

Mouth 1 20 

Tongue 120 

Palate 120 

Teeth 120 

Salivary  Glands 122 

Pharynx 122 

(Esophagus 122 

Abdominal  Cavity 123 

Stomach 123 

Small  Intestines 125 


CONTENTS.  Xlll 

PAGE 

Digestive  System,  Caecum 127 

Large  Colon 128 

Small  Colon 128 

Rectum 128 

Anus 128 

Liver 129 

Lobes 129 

Fissures 129 

Ligaments 129 

Parenchyma 129 

Pancreas 131 

Spleen 132 

Peritoneum 132 

Respiratory  Organs 133 

Larynx 133 

Cartilages 133 

Articulations 134 

Muscles 135 

Trachea 136 

Bronchi 138 

Lungs 138 

Pleura 139 

Thorax 140 

Mediastinae 140 

Ductless  Glands '. 140 

Thyroid 140 

Thymus 141 

Urinary  Organs 141 

Kidneys 141 

Supra-renal  Capsules 144 

Ureters 144 

Bladder 144 

Male  Genitals 145 

Testicles 145 

Descent  of 146 

Vas  Deferens 147 

Vesiculas  Seminales 147 

Prostate  Gland 148 

Urethra 148 

Penis 149 

Perineum 150 

Female  Genitals 150 

Vulva 150 

Vagina 151 

Uterus 152 

Oviducts 153 

Ovaries 153 

Mammary  Glands 155 

Organs  of  Special  Sense 155 

Smell 155 


XIV  CONTENTS. 

PAGE 

Organs  of  Special  Sense,  Nasal  Fossae 155 

Nostrils 156 


Taste . 


157 


Papillae  of 157 

Nerves  of 157 

Auditory  Organs 157 

External  Ear 157 

Cartilages  of 157 

Muscles  of 158 

Canal  of 159 

Middle  Ear. 159 

Internal  Ear 161 

Eye* 162 

Orbits 162 

Tunics 162 

Humors 162 

Muscles  of  Lid 165 

Globe 165 

Appendages 166 

Blood  Supply 167 

Skin  and  Appendages 167 

Hairs , 168 

Hoof 168 

Physiology 173 

Definition v 173 

Circulation 173 

Composition  of  Blood , 173 

Coagulation 174 

Circulation 175 

Velocity  of  Blood  Current 176 

Respiration 177 

Inspiration 177 

Muscles  of 177 

Expiration ' 178 

Muscles  of 1 78 

Nervous  Mechanism 1 79 

Alimentation 180 

Definition 180 

Digestion 180 

Food 181 

Prehension 181 

Mastication 182 

Salivary  Digestion 183 

Deglutition 183 

Gastric  Digestion 184 

Bile 185 

Tests  for 185 

Glycogenic  Function  of  Liver 186 

Pancreatic  Juice 186 


CONTENTS.  XV 

PAGE 

Intestinal  Juice 187 

Faeces 188 

Defecation 188 

Intestinal  Movements 188 

Absorption 188 

Lymph 189 

Chyle 189 

Animal  Heat 190 

Secretion 190 

Definition  of . * 190 

Excretion,  Definition  of 190 

Perspiration , 191 

Mammary  Secretion f .  .  .  191 

Urine 192 

Composition  of 192 

Amount  of,  in  Twenty-four  Hours 193 

Micturition 193 

Ductless  Glands 193 

Supra-renal  Capsules 193 

Spleen 194 

Thymus  and  Thyroid 194 

Pituitary  Body  and  Conarium 194 

Nervous  System 194 

Nerves,  Termination  of .  194 

Spinal 195 

Cranial 195 

Spinal  Cord 197 

Functions  of 198 

Columns  of 198 

Medulla  Oblongata 198 

Pons 199 

Corpora  Quadrigemina 199 

Optic  Thalami 199 

Olfactory  Lobes 199 

Cerebellum 199 

Cerebrum 199 

Sympathetic  System 200 

Special  Senses 200 

Touch 200 

Smell 200 

Taste 200 

Hearing 201 

Sight 201 

Reproduction,  Reference  to 202 


COMPLIMENTS 
OF 

F,  ElaHstou's  Son  Cfc, 


EQUINE 

ANATOMY  AND  PHYSIOLOGY. 


ANATOMY. 


Anatomy  is  the  science  of  organization. 

Equine  Anatomy  is  its  study  confined  to  the  horse. 

Divisions. 

Osteology,  the  study  of  bones;  Arthrology  or  Syndesmology, 
of  the  joints;  Myology,  of  the  muscles;  Angeiology,  of  the  vessels; 
Neurology,  of  the  nervous  system;  Splanchnology,  of  the  viscera. 

OSTEOLOGY,  OR  THE  BONES. 

See  plate  opposite  title  page. 

These,  the  passive  portion  of  the  locomotory  apparatus,  are 
divided  into  long,  short,  flat  and  irregular.  The  long  bones  are 
found  in  the  limbs  and  are  hollowed  out  internally;  example,  the 
femur.  The  short  bones  are  about  as  wide  as  long,  and  contain 
no  medullary  cavity;  example,  the  tarsus  and  carpus.  The  flat 
bones  are  found  in  the  head,  pelvis,  and  shoulder,  contain  no 
medullary  cavity,  and  are  not  thick;  examples,  the  parietal  and 
scapula.  The  irregular  bones  have  none  of  the  characteristics  of 
the  preceding;  example,  the  hyoid. 

The  Eminences  of  Bones. 

Heads  are  elevations  on  the  extremities  of  bones,  describing 
the  segment  of  a  sphere;  condyles  are  segments  of  an  oval  figure 
parallel  to  its  large  axis;  processes  or  apophyses  when  much  de- 


IO  EQUINE   ANATOMY. 

tached  from  bones;  protuberances  or  tuberosities  are  large  and 
round;  lines,  crests  and  ridges  are  narrow  and  long. 
Cavities  of  Bones. 

Cotyloid  are  deeply  excavated;  channels  or  furrows  when  wide 
and  deep;  fissures  when  narrow  and  rough;  digital  when  of  the 
size  of  finger-ends;  fossa,  sinuses,  cells  and  notches  are  also  cavi- 
ties.    An  opening  in  a  bone  is  a  foramen,  if  long,  a  canal. 
Composition  of  Bone. 

Botie   is   composed   of   one-third   part   animal   matter,   giving 
elasticity,  and  two-thirds  mineral  matter,  principally  salts  of  lime, 
giving  strength. 
Structure  of  Bone. 

Bones  are  covered  externally  by  a  fibrous,  nourishing  mem- 
brane, the  periosteum.  Microscopically  bone  is  seen  to  consist  of 
the  following  parts:  the  medullary  canal,  see  cavity  of  long  bones; 
the  Haversian  canals  for  the  passage  of  vessels;  lacuna,  small 
black  spaces  containing  bone  cells  with  little  canals,  the  canaliculi, 
branching  from  them;  these  three  structures  form  the  Haversian 
systems.  Lamellce  are  layers  of  bone  under  the  periosteum  or 
around  the  Haversian  canals. 

The  marrow  or  medulla  of  bones  consist,  of  red  or  fatal  marrow, 
and  yellow  marrow.     The  former  is  rich  in  round  cells,  the  latter 
in  fat. 
Development  of  Bone. 

It  may  be  developed  from  cartilage  or  membrane.     The  former 
method  is  shown  in  the  long,  the  latter  in  the  flat  bones. 
Number  of  Bones. 

Vertebral  column '. 52 

Head 8 

Face 16 

Hyoid,  sternum  and  ribs 38 

Anterior  extremities 40 

Posterior  extremities 4° 

419 
The  ossicles  of  the  middle  ear  are  not  included;  the  sacrum  is 
considered  as  five  separate  bones,  the  superior  turbinated  as  part 
of  the  ethmoid,  the  pterygoid  as  a  process  of  the  sphenoid,  the 
parietal  as  a  double  bone,  and  the  sesamoids  are  included. 


OSTEOLOGY.  I I 

THE  VERTEBRAL  COLUMN. 

The  spinal  column  is  composed  of  52  segments,  divided  into 
true  and  false. 

The  true  are  divided  into  7  cervical,  18  dorsal  and  6  lumbar. 
The  false  into  the  sacrum,  of  5  segments  closely  fused,  and  the 
coccyx,  of  from  15  to  18  segments  more  or  less  movable. 

Common  Characteristics  of  Vertebrae. 

Each  one  has  a  body  and  an  arch,  enclosing  the  spinal  canal, 
which  includes  the  spinal  cord.  The  body  has  a  superior  face, 
forming  the  lower  boundary  of  the  spinal  canal,  an  inferior,  two 
lateral  surfaces,  a  head,  convex  for  articulation,  an  anterior  extrem- 
ity, and  a  concave  posterior  extremity. 

The  arch  projects  upward  from  the  top  of  the  body,  and  con- 
sists of  pedicles,  lamina,  transverse,  spinous  and  articular  processes. 

The  pedicles  are  two  strong  processes  projecting  upward  and 
supporting  the  transverse  and  articular  processes. 

The  transverse  processes  project  laterally  from  the  summit  of 
the  pedicles.  They  are  elongated  antero-posteriorly  in  the  cerv- 
ical, short  in  the  dorsal,  and  long  in  the  lumbar  regions. 

The  laminoz  are  two  processes  uniting  above  and  forming  the 
spinous  process;  they  enclose  the  spinal  cord. 

The  spinous  processes  project  upward  and  backward,  from  the 
junction  of  the  laminae.  They  are  small  in  the  cervical,  long  in 
the  dorsal,  rough  and  enlarged  in  the  lumbar  regions. 

The  articular  processes  are  four  in  number,  two  anterior  and 
two  posterior.  The  former  look  upward,  the  latter  downward. 
In  each  is  a  notch,  which,  when  in  apposition,  forms  the  interverte- 
bral foramen. 

CERVICAL   REGION. 

Common  Characters. 

The  body  is  long  and  thick  and  has  an  inferior  spine. 

The  spinous  processes  are  a  roughened  line. 

The    transverse  or  trachelian  processes  are  elongated  antero- 
posteriorly  and  are  in  relation  to  the  trachea.     They  are.traversed 
at  their  base  by  a  foramen,  transmitting  vessels,  the  vertebral. 
The  articular  processes  look  downward  and  inward. 
Peculiar  Cervical  Vertebrae. 

The  1st  or  atlas  articulates  with  the  occipital,  has  a  thin  body, 


12  EQUINE   ANATOMY. 

no  head,  two  deep  concave  facets  in  its  place;  an  articular  sur- 
face below  for  the  odontoid  process;  transverse  process  very  rudi- 
mentary. The  spinous  processes  are  flattened  from  above,  down- 
ward, are  elongated  and  show  two  foramina,  the  anterior  trans- 
mitting a  vein,  the  posterior  the  vertebral  vessels. 

The  2d  or  axis  is  very  long,  has  no  head,  but,  in  its  place,  a 
process  convex  and  smooth  below,  concave  above,  articulating 
with  the  body  of  the  atlas,  called  the  odontoid  (or  tooth-like). 
The  spinous  process  is  very  elongated  antero-posteriorly  and 
divided  into  two  lips.     The  transverse  are  little  developed. 

The  $th  has  a  heart-shaped  tubercle  on  its  inferior  spine. 

The  6th  or  tricuspid  has  a  third  prolongation  on  its  transverse 
process. 

The  jth  or  prominens  has  a  long  spine,  demi-facets  behind  for 
the  i  st  rib,  the  transverse  processes  are  single,  and  the  vertebral 
foramen  is  absent. 

THE  DORSAL  VERTEBRA. 

The  body  is  short  with  a  projecting  head  anteriorly,  a  marked 
depression  posteriorly,  and  four  articular  cavities  for  the  heads  of 
the  ribs,  two  in  front,  two  behind.  The  spinous  processes  are  long, 
and  flattened  on  the  sides.  The  transverse  processes  are  short, 
and  have  a  facet  for  articulation  with  the  tuberosity  of  a  rib.  The 
length  of  the  spines  increases  to  the  5th  and  then  decreases  to 
the  1 8th.     The  18th  has  no  facet  on  its  body  behind. 

THE   LUMBAR  VERTEBRA. 

The  body  is  longer  and  wider  than  the  preceding,  the  spinous 
process  is  shorter  and  surmounted  by  a  tubercle;  the  transverse 
processes  are  flattened  from  above,  downward,  and  pass  trans- 
versely outward,  the  fifth  and  sixth,  and  sixth  and  front  of  the 
sacrum  articulating  by  facets. 

THE   SACRUM. 

The  sacrum  consists  of  five  segments,  closely  fused.  It  articu- 
lates with  the  last  lumbar  and  its  transverse  process  in  front,  the 
coccyx  behind  and  the  os  innominata  laterally. 

It  is  triangular  in  shape  with  a  base  anteriorly  articulating  with 
the  body,  articular  and  transverse  processes  of  the  last  lumbar; 
showing  also  the  vertebral  canal,  an  apex  behind  articulating 
with  the  coccyx,  two  lateral  borders  articulating  with  the  innominate 


OSTEOLOGY.  1 3 

bones  in  front,  an  inferior  surface  smooth  and  showing  four  inter- 
vertebral foramina,  and  a  superior  surface  showing  the  spinous 
process  and  the  supersacral  foramina. 

THE  COCCYX. 

This  consists  of  from  fifteen  to  eighteen  segments;  the  first 
three  or  four  only  are  complete,  the  spinal  canal  then  simply  con- 
tinuing as  a  groove.  The  first  is  often  consolidated  with  the 
sacrum. 

THE  HEAD. 

This  consists  of  eight  bones,  the  occipital,  two  parietal,  two 
temporal,  the  ethmoid,  frontal  and  sphenoid. 

OCCIPITAL. 

The  occipital  forms  the  upper  and  posterior  portion  of  the  head, 
and  is  divided  into  an  external  and  internal  face  and  circumference. 
The  External  Face  shows — 

The  external  occipital  protuberance,  an  elevation  forming  the 
point  of  the  head. 

The  occipital  foramen  (or  foramen  magnum)  below  and  in 
front  of  the  preceding,  a  large  round  opening,  transmitting  the 
spinal  cord,  its  membranes,  the  cerebro-spinal  vessels  and  eleventh 
nerve. 

The  basilar  process,  a  long  narrow  prolongation  passing  forward 
to  unite  with  the  body  of  the  sphenoid. 

Two  sharp  crests  running  outward,  the  superior,  continuing  as 
the  zygomatic  process,  the  inferior,  terminating  at  the  base  of  the 
styloid  process. 

The  two  condyles  which  lie  on  either  side  of  the  foramen,  articu- 
lating with  the  atlas. 

The  styloid  processes,  two  large  blunt  projections  lying  outside 
the  preceding. 

The  condyloid  foramina,  lying  at  the  bottom  of  a  fossa  under 
the  condyles  and  transmitting  the  twelfth  nerves. 

The  Internal  .Face  shows  the  foramen  magnum,  condyloid 
foramen,  and  a  smooth  roof  for  the  cranial  cavity. 

The  Circumference  shows — 

Articulations  above  for  the  parietal  bones,  and  laterally  for  the 
temporal. 


14  EQUINE   ANATOMY. 

A  deep  notch  closed  in  by  the  temporal  and  sphenoid,  forming 
the  anterior  and  posterior  lacerated  foramina,  separated  by  a  liga- 
ment. 

Articulations  6. 

Two  parietal,  two  temporal,  sphenoid  and  atlas. 

PARIETAL   (A  WALL). 

The  parietals  form  the  roof  of  the  cranial  cavity,  are  developed 
from  two  centres  closely  fused  together  and  closed  in  by  the  occip- 
ital, frontal,  temporal  and  opposite  parietal. 

It  has  external  and  internal  surfaces,  and  four  borders,  superior, 
inferior,  external  and  internal. 

The  external  surface  shows  the  parietal  ridge  beginning  at  the 
occipital  protuberance  and  ending  at  the  supra-orbital  process  of 
the  frontal.  It  divides  the  bone  into  two  rough  and  one  smooth 
portions. 

The  internal  surface  shows  depressions  for  the  brain  and  a 
marked  elevation,  the  parietal  eminence,  which  lodges  the  conflu- 
ence of  the  sinuses,  the  torcular  Herophili;  from  this  point  lateral 
ridges  run,  lodging  the  parieto-temporal  confluents.  In  front  it  is 
prolonged  by  the  suture  between  the  two  bones,  the  sagittal. 

The  superior  border  is  thick  and  articulates  with  the  occipital. 

The  inferior  border  articulates  with  the  frontal. 

The  internal  border  articulates  with  its  opposite. 

The  external  border  articulates  with  the  temporal  and  forms  a 
groove,  the  p&rieto-temporal  canal. 

Articulations  5. 

Occipital,   frontal,   sphenoid,    temporal   and   opposite. 

FRONTAL. 

The  frontal  (Jrons,  the  forehead)  forms  the  front  part  of  the 
roof  of  the  cranium  and  part  of  the  face.  It  lies  between  the 
parietals  above,  the  nasals  and  lachrymals  below,  and  the  tem- 
porals laterally. 

It  has  two  surfaces,  an  external  and  internal,  and  four  borders, 
a  superior,  inferior  and  two  lateral. 

The  External  Surface  shows — 

A  median  plane  surface  covered  with  skin  and  forming  the  base 
of  the  forehead.     Two  strong  processes  projecting  outward  form- 


OSTEOLOGY.  1 5 

ing  the  orbital  arch  and  articulating  externally  with  the  zygomatic 
process  of  the  temporal.  An  opening  in  the  orbital  arch,  the 
supra-orbital. 

At  the  base  of  the  arch  a  depression  for  the  pulley  of  the  superior 
oblique. 

The  Internal  Surface  is  concave  and  shows — 

A  superior  part  articulating  with  the  parietal  above  and  joining 
below  the  crista  galli  and  wing  of  the  sphenoid. 

An  inferior  part  articulating  in  the  median  line  with  the  ethmoid, 
and  shows  two  large  openings  into  the  frontal  sinuses,  two  spaces 
between  the  external  and  internal  plates  of  the  bone.  It  forms 
part  of  the  roof  of  the  nasal  fossae. 

The  superior  border  articulates  with  the  parietal  and  temporal, 
the  inferior  with  the  lachrymal  and  nasal,  and  the  lateral  with 
the  palate  and  sphenoid,  forming  with  the  latter  the  orbital 
foramen. 

The  frontal  has  two  centres  of  ossification. 
Articulations,  14. 

With  two  parietal,  two  temporal,  two  nasal,  two  lachrymal, 
sphenoid,  ethmoid,  two  palate  and  two  superior  maxillary. 

ETHMOID. 

The  ethmoid  (sieve-like)  lies  at  the  anterior  part  of  the  floor 
of  the  skull,  and  forms  part  of  the  roof  of  the  nasal  fossae. 

It  is  divided  into  a  vertical  plate,  a  horizontal  portion,  and  two 
lateral  masses. 

The  vertical  portion  articulates  below  with  the  vomer  and  the 
median  nasal  cartilage,  forms  the  median  septum  of  the  nose,  and 
terminates  above  in  the  crista  galli,  a  small  elevation  on  which  a 
process  of  the  cerebral  dura  mater  is  attached. 

The  horizontal  portion  forms  the  roof  of  the  nasal  cavities,  part 
of  the  cranial  floor,  and  is  perforated  by  a  number  of  openings 
for  the  passage  of  the  filaments  of  the  olfactory  nerves.  The 
lateral  masses  form  part  of  the  orbital  and  nasal  walls,  are  exca- 
vated to  form  the  ethmoidal  cells  and  show  an  anterior  projection 
forming  the  superior  turbinated  bone  which  is  really  a  part  of  the 
ethmoid  and  considered  as  such. 
Articulations,  7. 

Sphenoid,  frontal,  vomer,  two  palate,  two  superior  maxillary. 


1 6  EQUINE  ANATOMY. 

SPHENOID. 

The  sphenoid  (a  wedge)  serves  to  connect  the  bones  of  the  head 
and  face,  being  wedged  in  between  the  occipital  behind,  the 
ethmoid  and  frontal  in  front,  the  parietals  and  temporals  laterally. 
It  is  divided  into  a  body  and  two  wings. 

The  body  shows  on  its  internal  surface — 

The  optic  fossa,  a  transverse  depression  for  the  optic  nerves, 
ending  in  the  optic  foramina,  which  open  into  the  orbit. 

The  sella  turcica  or  pituitary  fossa,  behind  this,  receiving  the 
pituitary  body. 

The  wings  projecting  from  the  body  -and  articulating  with  the 
frontal. 

Two  fissures  outside  the  sella  turcica,  the  inner  one  lodging  the 
cavernous  sinus. 

The  supra-sphenoidal  canals,  the  upper  one  called  the  great 
sphenoidal  fissure,  the  lower  the  foramen  rotundum,  the  middle 
opening  near  the  optic. 

The  External  or  Inferior  Surface  shows — 

Outside,  the  vidian  canal  opening  into  the  orbit. 

The  internal  pterygoid  plate  (pterygoid  bone)  outside  the  vomer, 
flattened  laterally. 

Its  internal  face  forms  part  of  the  pharyngeal  walls. 

At  its  base  is  found  the  vidian  canal  (see  above). 

Its  apex  forms  the  hamular  (hooked)  process,  passing  back- 
ward and  serving  for  the  passage  of  the  tendon  of  the  tensor  palati. 

The  external  pterygoid  or  sub-sphenoidal  process  lying  outside 
the  preceding. 

Above  this  the  opening  of  the  sub-sphenoidal  canal  which  opens 
into  the  orbit. 

Below  two  fissures  for  articulation  with  the  vomer. 

The  superior  or  posterior  border  is  continuous  with  the  basilar 
process  of  the  occipital,  and  on  each  side  forms  the  inner  bound- 
aries of  the  lacerated  foramen.  Three  notches  are  also  seen,  for 
the  passage  of  the  carotid  artery,  the  foramen  ovale  for  the  infe- 
rior maxillary  nerve,  and  one  for  the  middle  meningeal  artery,  the 
foramen  spinosum. 

The  anterior  or  inferior  border  shows — 

The  sphenoidal  sinuses,  excavations  continuous  with  the  eth- 
moidal plate. 


OSTEOLOGY.  .  I 7 

The  lateral  borders  show — 

Thin  edges  for  articulation  with  the  frontal,  squamous  part  of 
the  temporal  and  parietal. 
Articulations,  10. 

Occipital,  ethmoid,  frontal,  vomer,  two  parietal,  two  temporal 
and  two  superior  maxillary. 

THE  TEMPORAL. 

The  Temporal  is  important  as  forming  the  bony  canals  for  the 
reception  of  the  organ  of  hearing,  and  is  found  forming  parts  of 
the  sides  of  the  head,  face  and  cranial  cavity. 

It  is  divided  into  squamous  and  tuberous  portions. 

The   Squamous  portion  is  flattened,  oval  in  shape,  forming 
part  of  the  lateral  cranial  wall,  and  is  divided  into  external  and 
internal  surfaces  and  a  circumference. 
The  External  Surface  shows — 

The  zygomatic  process,  passing  downward  and  forward,  and 
articulating  with  the  zygoma;  at  its  base  is  found  the  glenoid 
cavity  for  the  condyle  of  the  inferior  maxilla,  limited  in  front  and 
behind  by  two  marked  elevations. 
The  Internal  Surface  shows — 

The  groove,  which,  with  the  parietal,  forms  the  parieto-temporal 
canal  and  depressions  for  cerebral  convolutions. 

The  circumference  articulates  with  the  frontal,  parietal,  sphenoid 
and  occipital. 

It  is  not  united  to  the  tuberous  portion. 

The  Tuberous  portion  passes  forward  and  inward  between 
the  occipital  and  parietal,  and  is  divided  into  petrous  and  mastoid 
processes. 

The  petrous  portion  shows — 

An  anterior  face  in  contact  with  the  parietal. 

A  posterior  face  in  contact  with  the  occiput. 

An  internal  face  which  shows  the  internal  auditory  meatus,  the 
entrance  of  the  seventh  nerve  to  the  internal  ear,  and  the  opening 
of  the  aqueductus  fallopii. 

An  anterior  border  separating  the  cerebral  from  the  cerebellar 
cavities. 

The  mastoid  portion  forms  the  base  of  the  horizontal  part  of 
the  bone  and  shows — 


1 8  .  EQUINE   ANATOMY. 

The  external  auditory  meatus,  a  round  opening  leading  into  the 
auditory  canal. 

The  mastoid  process,  a  round  eminence  behind  the  preceding, 
hollowed  out  with  cells,  communicating  with  the  middle  ear. 

The  stylo-mastoid,  in  front  of  the  preceding. 

Below,  the  styloid  process  for  the  origin  of  the  Tensor  Palati 
and  Eustachian  tube. 

The  hyoid  or  vaginal  process,  a  small  elevation. 

Articulations  7. 

Occipital,  parietal,  frontal,  sphenoid,  zygoma,  superior  maxilla 
and  inferior  maxilla. 

THE   FACE. 

This  consists  of  16  bones,  viz.,  two  superior  maxillary,  two  in- 
ter-maxillary, two  palate,  two  zygomas,  two  lachrymals,  two  nasals, 
two  inferior  turbinated,  one  vomer  and  one  inferior  maxillary. 
The  pterygoid  bones  are  considered  parts  of  the  sphenoid,  the 
superior  turbinated  parts  of  the  ethmoid,  and  the  hyoid  not  as 
belonging  to  the  face. 

THE   SUPERIOR  MAXILLA. 

These  two  large  bones  form  the  greater  part  of  the  structure  of 
the  face,  and  are  wedged  in  between  the  frontal,  nasal  zygomas, 
palates,  lachrymal  and  vomer. 

It  is  divided  into  two  faces,  two  borders,  and  two  extremities. 

The  External  Face  shows — 

A  convex  surface  ending  below  in  the  super-maxillary  spine,  a 
long  ridge  continuous  with  the  zygoma. 
The  orifice  of  the  intra-orbital  canal. 

The  Internal  Face  shows — 

The  flat  surface,  forming  the  outer  wall  of  the  nasal  fossa. 

A  deep  excavation,  the  maxillary  sinus. 

A  fissure  which  forms  the  palatine  canal. 

A  ridge  for  the  inferior  turbinated. 

The  inferior  opening  of  the  lachrymal  canal. 

The  palatine  process,  uniting  with  the  opposite,  forming  the 
floor  of  the  nasal  fossa. 

Anterior  border  shows — 


OSTEOLOGY. 


19 


Articular  processes  for  the  nasal,  pre-tnaxillary,  lachrymal  and 
palate  bones. 

External  border  shows — 

Six  cavities  for  the  molar  teeth,  behind  them  the  alveolar 
tuberosity.     Below,  the  small  interdental  space. 


Fig.  i. 


LATERAL   VIEW    OF  THE   HORSES    SKULL. 

Premaxillary  bone;  2,  Upper  incisors;  3,  Upper  canine  teeth;  4.  Superior  maxillary 
bone;  5,  Infraorbital  foramen;  6,  Superior  maxillary  spine;  7,  Nasal  bones;  8, 
Lachrymal  bone;  9,  Orbital  cavity;  10,  Lachrymal  fossa;  n,  Malar  bone;  12, 
Upper  molar  teeth;  13,  Frontal  bone;  15,  Zygomatic  process,  or  arch;  16,  Parietal 
bone;  17,  Occipital  protuberance;  18,  Occipital  crest;  19,  Occipital  condyles;  20, 
Styloid  processes;  21,  Petrous  bone;  22,  Basilar  process;  23,  Condyle  of  inferior 
maxilla;  24,  Parietal  crest;  25,  Inferior  maxilla;  26,  Inferior  molars;  27,  Anterior 
maxillary  foramen;  28,  Inferior  canine  teeth;  29,  Inferior  incisor  teeth. 


Superior  extremity  shows — 

A  rounded  enlargement,  lodging  the  maxillary  sinus. 

The  infra-orbital  canal,  running  above  the  molar  teeth,  ending 
opposite  the  third  molar  by  one  opening,  the  other  extending 
into  the  interior. 

The  palatine  canal,  between  the  bone  and  palate,  ending  at  the 
palatine  fissure. 

Inferior  extremity  shows — 

A  cavity  for  the  tusk,  uniting  with  the  pre-maxillary. 


20  EQUINE   ANATOMY. 

Articulations,  8. 

Opposite,  palate,  pre-maxillary,  ethmoid,  lachrymal,  nasal, 
inferior  turbinated,  zygoma. 

PRE-MAXILLARY   OR  INTER-MAXILLARY. 

The  pre-maxillaries  are  two  bones  lying  at  the  inferior  portion 
of  the  face  and  wedged  in  anterior  to  the  superior  maxillaries  and 
nasals. 

They  each  show  a  base  and  two  processes. 

The  base  shows — 

An  external  smooth  or  labial  face. 

An  internal  face,  united  with  the  opposite,  and  showing  the 
incisive  foramen. 

A  posterior  or  buccal  face,  forming  the  roof  of  the  mouth. 

An  external  border,  showing  three  sockets  for  the  incisors,  the 
inter-space  and  a  half  socket  for  the  tusk. 

An  external  process  passes  upward  between  the  nasal  and  super- 
maxillary,  forming  part  of  the  nose  and  face. 

An  internal  process  forms  part  of  the  nasal  floor  and  buccal 
roof.    It  forms,  also,  the  deep  incisive  notch. 

Articulations  4. 

Opposite,  superior  maxillary,  nasal,  vomer. 

PALATE. 

The  palates,  two  in  number,  at  the  back  part  of  the  nasal  and 
oral  cavities,  are  elongated  from  above  downward,  and  show  two 
faces,  two  borders  and  two  extremities,  a  superior,  united  with  the 
sphenoid,  and  an  inferior,  united  with  the  opposite. 

The  External  Face  shows — 

A  superior  orbital,  inferior  palatine,  forming  the  roof  of  the 
palate,  and  middle  articular,  for  the  superior  maxillary,  portions. 

The  internal  face  forms  part  of  the  outer  nasal  wall. 

The  anterior  border  shows — 

A  deep  foramen,  the  nasal,  an  articulation  for  the  super-maxil- 
lary, and  a  cavity  uniting  with  the  sphenoidal  sinus. 

The  posterior  border  shows — 

The  palatine  crest  above,  and  a  surface  for  the  external  pterygoid 
plate. 


OSTEOLOGY.  21 

Articulations,  7. 

Superior  maxillary,  sphenoid,  inferior  turbinated,  vomer,  ethmoid, 
frontal  and  opposite. 

ZYGOMATIC   OR  MALAR. 

The  zygomas  form  part  of  the  side  of  the  face,  wedged  in  between 
the  superior  maxilla,  frontal  and  zygomatic  process  of  the  tem- 
poral. It  has  a  base,  united  with  the  superior  maxillary,  a  sum- 
mit, united  with  the  zygomatic  process,  an  external  face,  internal 
face,  anterior  and  posterior  border. 

The  external  face  has  a  smooth  portion  forming  part  of  the 
orbital  margin  and  a  smooth  convex  facial  portion. 

The  internal  face  shows  an  articulation  for  the  superior  maxilla. 

The  anterior  border  joins  the  lachrymal,  the  posterior  or  mas- 
seteric forms  a  ridge  continuous  with  that  of  the  superior  maxilla. 
Articulations,  3. 

Superior  maxillary,  temporal  and  lachrymal. 

LACHRYMAL. 

The  lachrymal  is  a  quadrilateral  bone  forming  parts  of  the  face 
and  orbit,  bent  on  itself  and  wedged  between  the  frontal,  nasal, 
malar  and  superior  maxilla.  It  shows  external  and  internal 
surfaces,  and  a  circumference  articulating  with  the  surrounding 
bones. 

The  external  surface  shows — 

A  superior  or  orbital  portion,  concave,  and  forming  the  upper 
extremity  of  the  lachrymal  duct  and  fossa. 

An  inferior  or  facial  convex  portion. 

The  internal  surface  forms  part  of  the  maxillary  and  frontal 
sinuses. 

Articulations,  4. 

Frontal,  nasal,  superior  maxilla  and  malar. 

NASAL. 

The  nasal  bones  are  two  in  number,  articulating  with  each 
other  in  the  median  line,  and  forming  the  bony  framework  of  the 
nose. 

They  are  triangular  in  shape,  with  their  base  upward  uniting 
with  the  frontal,  the  apex  downward  and  pointed,  forming  the 
nasal  prolongation. 


2  2  EQUINE   ANATOMY. 

It  also  shows  an  external  and  internal  face,  an  external  and 
internal  border. 

The  external  face  is  convex  from  side  to  side  and  smooth. 

The  internal  face  gives  attachment  to  the  ethmoid,  and  is  covered 
with  mucous  membrane. 

The  external  border  unites  with  the  lachrymal,  superior  and 
inter- maxillaries,  the  internal  with  the  opposite  nasal. 
Articulations,  5. 

Frontal,  lachrymal,  superior  maxillary,  inter -maxillary  and 
opposite. 

INFERIOR  TURBINATED. 

These  two  scroll-shaped  bones  are  attached  to  the  superior 
maxilla  and  palate,  and  rolled  from  behind  forward.    It  separates 
the  middle  from  the  inferior  nasal  meatus. 
Articulations,  2. 

Superior  maxilla  and  palate. 

VOMER. 

The  vomer  is  a  single  bone  in  the  median  facial  line,  forming 
part  of  the  nasal  septum,  and  attached  above  to  the  sphenoid  by 
its  upper  extremity,  which  is  divided  into  two  narrow  processes. 
Its  lower  extremity  is  attached  to  the  superior  maxillary  palate 
and  pre-maxillary  bones.  Its  two  lateral  faces  are  smooth  and 
covered  with  mucous  membrane. 
Articulations,  8. 

Sphenoid,  ethmoid,  two  superior  maxillary,  two  pre-maxillary 
and  two  palate. 

INFERIOR  MAXILLA. 

The  lower  jaw  is  a  large  bone  forming  the  inferior  and  anterior 
part  of  the  face,  and  articulating  with  the  two  temporal  bones. 
It.  is  convex  externally,  concave  internally,  forming  the  inter- 
maxillary space.  It  consists  of  two  extremities,  an  inferior  and 
superior,  two  faces,  external  and  internal,  and  two  borders,  a 
superior  and  inferior. 

The  inferior  extremity  shows — 

The  union  of  the  two  lateral  halves  of  the  bone. 

An  inferior  or  labial  face,  smooth  and  convex,  containing  the 
opening  of  the  mental  foramen  on  the  sides;  at  this  point  it  is 
constricted,  the  neck. 


OSTEOLOGY.  23 

A  superior  or  concave  buccal  face,  supporting  the  tongue. 

A  circumference,  convex  anteriorly,  with  sockets  for  the  six 
incisors,  and  behind  these  for  the  two  tusks. 

The  space  between  the  lateral  incisors  and  tusks,  is  called  the 
dental  interspace  or  bars. 

The  superior  extremity  shows — 

The  condyloid  process  elongated  transversely  for  articulation 
with  the  glenoid  cavity  of  the  temporal. 

The  neck,  a  constriction  below  this. 

The  coronoid  process,  in  front  of  the  condyle,  separated  from 
it  by  the  sigmoid  notch,  is  flattened  on  its  sides,  and  receives  the 
insertion  of  the  temporal  muscle. 

The  external  face  shows — 

A  smooth  surface  below,  a  rough  one  above,  for  the  masseter. 

The  internal  face  shows — 

In  its  upper  one-third  the  entrance  of  the  inferior  maxillo- 
dental  canal,  which  runs  down  under  the  teeth,  giving  off  another, 
the  mental  foramen  (see  above),  and  then  continued  in  the  bone 
under  the  incisors. 

A  smooth  surface  in  its  lower  two-thirds. 

The  mylo-hyoid  ridge,  a  line  running  parallel  with  and  below 
the  teeth. 

The  genial  surface,  a  rough  spot  at  the  junction  of  the  two 
sides. 

The  anterior  border  shows — 

The  alveolar  surface,  already  described,  and  a  thin  portion  for 
muscular  insertion. 

The  posterior  border  shows — 

A  sharp  straight  portion  and  a  more  rounded  portion  above, 
changing  its  direction  at  this  point.  It  is  there  called  the  angle. 
Articulations,  2. 

The  temporals. 

THE   FOSS.E. 

The  cranial  cavity  is  oval  in  form,  the  walls  formed  by  the 
frontal,  parietals  and  occipital  above;  the  occipital,  parietals,  tem- 
porals and  sphenoid  on  the  sides;  the  occipital  basilar  process,  the 
sphenoidal  body,  the  transverse  portion  of  the  ethmoid,  and  in- 
ternal surface  of  the  frontal  below. 

It  is  divided  into  anterior  or  cerebral  and  posterior  or  cerebellar 


24  EQUINE   ANATOMY. 

fossae  by  the  petrous  portion  of  the  temporal.  In  the  posterior 
fossa  is  the  foramen  magnum,  the  communication  between  the 
spinal  and  cerebral  cavities. 

Contents — cerebrum,   cerebellum,   cranial  nerves  and  vessels. 

The  orbital  cavity  and  nasal  fossa  are  described  with  the  special 
senses  of  sight  and  smell. 

The  temporal  fossa,  oval  in  shape,  lie  behind  the  orbit,  on  the 
outer  cranial  wall,  bounded  within  by  the  parietal  ridge,  without 
by  the  zygomatic  process. 

They  lodge  the  temporal  muscle,  coronoid  process  and  vessels. 

THE   HYOID. 

The  hyoid  bone  consists  of  seven  segments,  lying  below  the 
head,  above  the  larynx  and  under  the  tongue,  in  the  inter-maxil- 
lary space. 

It  consists  of  a  body,  two  thyroid  or  great  cornua,  two  styloid  or 
lesser  cornua,  and  two  styloid  bones. 

The  body  is  convex  in  front,  concave  behind,  with  two  lateral 
prolongations,  continuous  with  the  thyroid  cornua,  and  an  ante- 
rior appendix,  projecting  into  the  muscular  structure  of  the  tongue. 

The  thyroid  or  great  cornua  project  backward,  articulating  with 
the  extremities  of  the  thyroid  cartilage. 

The  styloid  or  lesser  cornua  are  small,  and  articulate  below 
with  the  body  at  its  junction  with  the  great  cornua.  It  often  has 
a  cartilaginous  nodule  at  its  inferior  extremity,  the  styloid  nucleus. 

The  styloid  bones  are  long,  flattened  on  the  sides,  articulating 
above  with  the  hyoideal  prolongation  of  the  temporal,  below  with 
the  lesser  cornua.  They  represent  the  styloid  process  and  stylo- 
hyoid ligament  of  man. 

THE   STERNUM. 

The  sternum  forms  the  inferior  boundary  of  the  thoracic  cavity, 
showing  on  either  side  articulations  for  the  first  eight  ribs.  It 
shows  an  anterior  extremity,  the  cervical  prolongation,  and  a 
posterior,  the  abdominal  prolongation  or  xiphoid  appendix. 

It  is  flattened,  laterally,  in  its  anterior  two-thirds,  and  from 
above  downwards  in  its  posterior  one-third. 
Articulations,  16. 

With  eight  anterior  ribs  on  either  side. 


OSTEOLOGY. 


25 


THE  RIBS. 

The  ribs  are  36  in  number,  18  on  either  side,  forming  the  lat- 
eral boundaries  of  the  thorax,  terminating  below  by  cartilaginous 
prolongations,  the  costal  cartilages.  They  articulate  above  with 
the  dorsal  vertebrae.  They  are  divided  into  sternal  or  true,  eight 
in  number,  and  asternal  or  false,  the  posterior  ten. 

General  Characteristics. — Each  rib  has  an  external  convex 
and  internal  concave  smooth  surface  and  an  anterior  or  convex 
border,  a  posterior  border,  showing  a  groove  for  the  intercostal 
vessels  and  nerves,  a  shaft  and  two  extremities. 

The  superior  extremity  articulates  with  the  vertebral  column, 
and  shows  a  head  with  two  demi-facets  for  the  bodies  of  the  ver- 
tebrae in  front  and  behind,  a  neck  below  the  head,  and  a  tuber- 
osity for  articulation  with  a  dorsal  transverse  process. 

The  inferior  extremity  is  excavated  for  the  cartilage. 

The  costal  cartilages  are  flattened  laterally,  the  first  eight  lying 
on  the  sternum,  the  remainder  articulating  with  the'  cartilage  in 
front. 

The  length  of  the  ribs  increases  from  the  first  to  the  9th,  then 
decreases;  their  width  from  the  1st  to  the  6th,  then  decreases. 

The  1st  rib  has  no  outer  groove  and  no  notch  on  its  head.  Its 
cartilage  is  short  and  thick,  and  has  an  articular  facet  below  for 
the  opposite. 

The  18th  rib  has  no  external  channel,  and  the  facet  on  its  tuber- 
osity is  confounded  with  that  of  its  head. 

For  thorax  see  Lungs. 

THE  ANTERIOR  EXTREMITY. 

This  is  divided  into  the  shoulder,  arm,  forearm  and  forefoot  or 
hand. 

THE   SHOULDER. 

In  solipedes  this  consists  of  the  scapula  only,  the  clavicle  being 
absent. 

THE   SCAPULA. 

The  scapula  or  shoulder  blade  is  a  flat,  triangular  bone,  lying  at 
the  anterior  and  inferior  part  of  the  outer  thoracic  wall,  articula- 
ting below  with  the  head  of  the  humerus.  Its  general  direction  is 
downward  and  forward. 

It  has  two  surfaces,  external  and  internal,  three  angles,  anterior 
3 


26  EQUINE   ANATOMY. 

or  cervical,  posterior  or  dorsal,  and  inferior  or  humeral,  and  three 
borders,  anterior,  posterior,  and  superior. 

'  The  external  surface  shows  two  cavities,  giving  attachment  to 
the  antea  and  postea-spinati  muscles,  divided  by  a  marked  crest, 
the  spine,  running  in  its  long  axis;  elevated  in  its  middle,  the  tu- 
berosity. 

The  internal  surface  is  concave,  forming  the  sub-scapular  fossa 
for  the  muscle  of  the  same  name. 

The  anterior  or  cervical  angle  is  thin;  the  posterior  thick. 

The  inferior  or  humeral  angle  has  a  constricted  neck;  below 
this  the  glenoid  cavity,  a  round,  shallow  depression,  for  the  humeral 
head. 

In  front  of  the  cavity  is  the  coracoid  process,  with  a  base  and  a 
summit  curved  inwardly. 

The  superior  border  is  prolonged  by  a  well-marked,  flattened 
cartilage. 

The  anterior  border  is  sharp  and  thin;  the  posterior,  thicker  and 
concave. 

It  articulates  with  the  humerus. 

THE   ARM. 

The  single  bone  forming  the  arm  is  the  humerus. 

THE   HUMERUS. 

The  humerus  is  a  long  bone,  articulating  above  with  the  scapula, 
below  with  the  ulna  and  radius.  It  has  a  shaft,  an  upper  and  a 
lower  extremity. 

The  shaft  has — 
|    An  anterior  surface,  showing  below  some  muscular  imprints. 

A  posterior  surface,  smooth  and  rounded. 

An  external  surface,  which  shows  a  groove,  winding  from  above 
downward,  and  behind  forward,  called  the  furrow  of  torsion,  and 
is  bounded  in  front  by  an  anterior  crest,  behind  by  the  posterior 
crest. 

The  anterior  crest  ends  below,  at  the  junction  of  the  upper  and 
middle  thirds,  in  the  deltoid  imprint,  a  rough  and  prominent  ele- 
vation, with  a  concavity  toward  the  furrow  of  torsion.  The 
furrow  of  torsion  lodges  the  short  flexor  of  the  forearm. 

The  internal  surface  is  rounded,  and  has,  at  its  middle,  a  rough 
depression  for  the  teres  major  and  latissimus  dorsi.  The  nutrient 
foramen  is  at  its  lower  third. 


OSTEOLOGY.  27 

The  superior  extremity  has — 

A  convex  head  for  articulation  with  the  glenoid  cavity. 

An  external  or  great  tuberosity,  which  shows  a  summit,  crest  and 
convexity. 

An  internal  or  small  tuberosity,  receiving  the  insertion  of  the 
sub  scapular  is. 

The  bicipital  groove,  between  the  two  tuberosities,  and  running 
downward.  It  consists  of  two  grooves  and  a  central  elevation, 
which  allow  the  passage  of  the  fibro-cartilaginous  tendon  of  the 
biceps. 

The  inferior  extremity  has — 

A  transversely  elongated  articular  process,  convex  from  before 
backward,  and  divided  into  two,  a  larger  internal  one,  the  trochlea, 
and  a  smaller  external,  the  condyle;  behind  and  above  this  a  depres- 
sion, which  receives  the  beak  of  the  olecranon  in  extension,  called 
the  olecranon  fossa.  In  front  and  to  the  inner  side,  another, 
the  coronoid  fossa,  which  receives  the  coronoid  in  flexion.  On 
the  inner  side,  above  the  trochlea,  the  epi-trochlea,  a  bony  eleva- 
tion.    On  the  outer  side,  in  the  same  position,  the  epi-condyle. 

Articulations,  3. 

Scapula,  radius  and  ulna. 

THE   FOREARM. 

This  consists  of  two  bones,  the  radius  and  ulna,  united  into 
one  at  an  early  age. 

THE   RADIUS. 

The  radius  is  a  long  bone  articulating  above  with  the  humerus, 
and  below  with  the  carpus. 

It  shows — 

An  external  and  internal  border,  thick  and  rounded. 

An  anterior  surface,  smooth  and  convex. 

A  posterior  surface,  concave,  with  a  rough,  triangular  surface 
from  the  upper  to  the  lower  fourth,  for  attachment  of  the  interos- 
seous ligament;  above,  a  transverse  groove,  to  form  the  radio- 
ulnar arch,  a  rough  spot  at  its  inferior  third. 

The  superior  extremity  shows — 

An  articular  surface,  smooth  and  concave,  divided  into  a  double 
depression  externally,  a  middle  ridge,  and  an  internal  depression. 

A  well-markedj^/ermz/  tuberosity. 


28  EQUINE  ANATOMY. 

The  internal  or  bicipital  tuberosity,  for  attachment  of  the  coraco- 
radialis. 

Below  this,  a  transverse  groove,  for  the  short  flexor  of  forearm. 

The  coronoid  process,  a  small  projection  anteriorly. 

Two  facets,  posteriorly,  for  the  ulnar  articulation. 

The  inferior  extremity  show&— 

Below,  the  articulating  surface  for  the  four  upper  carpus. 

Two  tubercles  for  ligaments,  externally  and  internally. 

Three  grooves  anteriorly,  the  two  outer  ones  lodging  the  ante- 
rior extensors  of  the  phalanges'  and  metacarpus;  the  internal  oblique 
one,  the  obilque  extensor. 

A  strongly  marked  ridge  behind,  for  ligaments. 
Articulations,  6. 

Humerus,  ulna,  pisiform,  cuneiform,  semi-lunar  and  scaphoid. 

THE   ULNA. 

The  ulna  is  a  long  bone  forming  the  posterior  and  upper  three- 
fourths  of  the  forearm,  and  strongly  united  to  the  radius. 

It  has  a  shaft,  an  upper  and  lower  extremity. 

The  shaft  is  triangular,  and  has — 

An  external  smooth,  internal  concave,  and  an  anterior  rough 
surface.  The  latter  shows  two  facets  and  the  ulnar  groove  for  the 
radio-ulnar  arch. 

There  are  also  two  lateral,  and  a  posterior  rough,  borders. 

The  upper  extremity  shows — 

A  Superior  enlargement,  the  olecranon  process,  for  the  attach- 
ment of  the  extensors  of  the  forearm.  This  has  external  convex 
and  internal  concave  surfaces. 

Its  anterior  portion  shows  a  deep  notch,  the  sigmoid  cavity,  for 
articulation  with  the  humerus,  terminating  above  in  the  beak. 

The  inferior  extremity  shows — 

A, small  knob,  the  capitellum,  which  sometimes  reaches  to  the 
end  of  the  radius. 
Articulations,  2. 

The  humerus  and  radius. 

THE   FORE-FOOT,    OR   HAND. 

This  comprises  in  the  horse  the  carpus,  seven  in  number,  three 
metacarpus,  three  phalanges  and  three  sesamoids. 


OSTEOLOGY.  20. 

THE  CARPUS. 

The  carpus,  seven  in  number,  are  divided  into  a  superior  and 
an  inferior  row. 

The  superior  row  are  named  from  without  inward — the  (i) 
pisijorm  or  super-carpal,  (2)  cuneiform,  (3)  semi-lunar,  and  (4) 
scaphoid. 

The  inferior  row  are  named — 

(1)  Unciform,  (2)  os  magnum  and  (3)  trapezoid. 

The  (1)  super-carpal  has  an  external  convex  face,  an  internal 
concave  /a<;e  and  a  circumference,  free  except  anteriorly,  where  it 
articulates  with  the  radius  and  cuneiform. 

The  (2)  cuneiform  is  wedge-shaped,  and  articulates  with  the 
radius,  super-carpal,  semi-lunar,  and  unciform. 

The  (3)  semi-lunar  is  half-moon  shaped  and  articulates  with 
the  cuneiform,  scaphoid,  radius,  unciform  and  magnum. 

The  (4)  scaphoid  is  boat-shaped  and  the  largest  of  the  row, 
articulating  with  the  radius,  semi-lunar,  magnum  and  trapezoid. 

The  unciform  is  hook-shaped  and  articulates  with  the  cunei- 
form,   semi-lunar,    magnum,    external   and    middle   metacarpals. 

The  (2)  05  magnum,  the  largest,  articulates  with  the  semi-lunar, 
scaphoid,  unciform,  trapezoid,  internal  and  middle  metacarpals. 

The  (3)  trapezoid,  resembling  the  same  geometrical  figure,  articu- 
lates with  the  scaphoid,  magnum,  middle  and  internal  metacarpals . 

THE   METACARPUS. 

This  region  consists  of  three  portions,  the  middle  or  principal, 
and  two  lateral,  the  external  and  internal  metacarpals. 

The  principal  metacarpal  shows — 

A  shaft,  smooth  and  rounded  in  front,  flattened  behind,  with  ar- 
ticular surfaces  on  each  side  for  the  rudimentary  bones;  at  its 
upper  third  the  nutrient  foramen. 

An  upper  extremity  articulating  with  the  inferior  carpal  row. 

An  inferior  extremity,  showing  two  articular  condyles  separated 
by  a  median  ridge.     On  each  side  are  ligamentous  depressions. 

The  rudimentary  metacarpals  (or  splint-bones)  show  a  superior 
extremity  articulating  with  the  inferior  carpal  row,  an  inferior 
extremity  extending  as  far  as  the  lower  fourth  of  the  middle  bone 
and  ending  in  a  button  and  a  shaft  with  three  surfaces,  an  anterior, 
articulating  with  the  middle,  external  and  internal  smooth  ones. 

The  internal  is  the  thicker  and  longer,  and  has  two  articular 
facets  above. 


30  EQUINE   ANATOMY. 

THE  PHALANGES. 

THE   FIRST   PHALANX   (OR  PASTERN  BONE). 

The  -first  phalanx  lies  between  the  principal  metacarpal  and  the 
second  phalanx,  and  has  a  shajt  and  two  extremities. 

The  shajt  has  an  anterior  convex  surface,  a  posterior,  flattened 
and  rough,  and  two  thick  borders. 

The  upper  extremity  has  two  articular  depressions,  separated  by 
a  ridge. 

The  inferior  extremity  has  two  condyles,  separated  by  a  groove 
and  laterally  two  ligamentous  depressions. 

SECOND   PHALANX   (OR   OS   CORONA ). 

The  second  phalanx  is  a  short  bone  with  two  articular  depres- 
sions above,  two  articular  processes  below,  an  anterior  face  with 
imprints,  and  a  posterior  face  with  a  transverse  gliding  surface. 
Articulations. 

First  phalanx,  third  phalanx  and  navicular  bone. 

THIRD   PHALANX   (OR   OS   PEDIS). 

The  third  phalanx  supports  the  hoof  and  anterior  limb.  It  is 
somewhat  pyramidal  in  shape,  and  is  divided  into  three  faces, 
three  angles,  and  two  lateral  borders. 

The  anterior  face  is  perforated  for  vessels  and  shows  laterally 
the  pre-plantar  fissure  between  the  basilar  and  retrossal  processes; 
the  patilobe  eminence  below  the  fissure. 

The  superior  face  shows — , 

Two  articular  cavities  separated  by  a  ridge,  for  the  second 
phalanx. 

The  inferior  (or  solar)  face  shows — 

A  flat  surface  below,  on  which  the  foot  rests,  a  curved  line,  the 
semi-lunar  crest,  and  laterally  two  channels,  the  plantar  fissures, 
opening  into  a  cavity  in  the  interior,  the  semi-lunar  sinus. 

The  superior  border  has  its  convexity  forward,  and  shows  the 
pyramidal  eminence  for  muscular  insertion. 

The  inferior  border  is  convex   and  perforated  by  foramina. 

The  posterior  border  shows  a  facet  for  the  navicular  bone. 

The  lateral  angles  show  two  posterior  projections,  a  superior, 
the  basilar,  and  inferior,  retrossal  processes.  Between  the  two  is 
the  origin  of  the  pre-plantar  fissure. 


OSTEOLOGY.  3 I 


THE  SESAMOIDS. 


The  sesamoids  consist  of  two  superior  or  large,  and  one  inferior, 
small  or  navicular  bone. 


THE   LARGE   SESAMOIDS. 


These  are  two  in  number,  lying  side  by  side  behind  the  superior 
part  of  the  first  phalanx.  Each  one  is  pyramidal,  and  has  an 
anterior  face  articulating  with  the  metacarpal,  a  posterior,  smooth 
for  the  gliding  of  tendons,  a  lateral  face,  a  base  and  summit. 

They  articulate  with  the  metacarpal  and  first  phalanx. 

THE  NAVICULAR  BONE. 

The  small  sesamoid  bone  lies  behind  the  third  phalanx,  to 
which  it  is  attached.  It  is  long  transversely  and  narrow,  and 
shows  a  superior  surface,  articulating  with  the  second  phalanx; 
an  anterior  surface,  articulating  with  the  third  phalanx;  an  in- 
ferior surface,  a  posterior  border  and  two  extremities. 

THE  POSTERIOR  EXTREMITY. 

This  is  divided  into  the  pelvis,  thigh,  leg,  and  foot. 

THE   PELVIS. 

The  pelvis  is  a  bony  cavity  containing  the  sexual  organs  and 
termination  of  the  internal  tract.  It  is  formed  above  by  the 
sacrum  laterally,  and  below  by  the  os  innominata. 

The  os  innominata  are  two  bones,  each  one  composed  of  three 
segments  closely  fused  together.  In  early  life  the  innominata 
bones  are  separate,  but  they  are  completely  joined  as  age  advances. 
They  consist  of  three  segments,  the  ilium,  ischium  and  pubes. 

THE  ILIUM. 

The  ilium  is  flat  and  triangular,  and  corresponds  internally  to 
the  sides  of  the  sacrum.  It  has  two  surfaces,  three  borders,  and 
three  angles.  The  external  surface  is  rough,  the  internal  surface 
shows  an  external  smooth  and  internal  rough  portion,  the  auric- 
ular surface  for  articulation  with  the  ilium.     The  anterior  border 


32  EQUINE   ANATOMY. 

is  rough,  the  external  thick  and  concave,  the  internal  thin  and 
concave,  forming  the  great  sciatic  notch. 

The  external  angle,  or  anterior  superior  spinous  process  is  thick, 
wide  and  flat,  and  called  the  angle  of  the  haunch.  The  internal 
or  posterior  superior  spine  curving  backward  and  upward,  is  called 
the  angle  of  the  croup.  The  posterior  angle  forms  part  of  the 
cotyloid  cavity;  above  this  cavity  is  the  supra-cotyloid  crest,  two 
rough  points  for  origin  of  the  rectus,  and  ilio- pectineal  eminence 
at  the  junction  with  the  pubes. 

THE   PUBIS. 

The  pubis  is  flattened  from  above  down,  elongated  transversely, 
and  has  two  surfaces,  three  borders  and  three  angles.  It  lies  inside 
the  ilium  and  in  front  of  the  ischium. 

The  superior  or  pelvic  surface  forms  the  pelvic  floor,  and  is 
smooth  and  concave. 

The  inferior  surface  is  rough  and  convex  and  shows  a  groove 
for  the  pubio-femoral  ligament. 

The  anterior  border  is  rough,  the  internal  is  united  with  the 
opposite  to  form  the  symphysis,  and  the  posterior  forms  the 
anterior  boundary  of  the  obturator  foramen. 

The  external  or  cotyloid  angle  forms  the  bottom  of  the  cotyloid 
cavity. 

The  internal  unites  with  the  opposite. 

The  posterior  is  united  with  the  ischium. 

THE   ISCHIUM. 

The  ischium  lies  behind  the'pubes  and  ilium,  and  is  the  smallest 
of  the  three  portions. 

It  has  two  surfaces,  a  superior  or  pelvic,  smooth,  and  an  inferior, 
rough,  four  borders  and  four  angles. 

The  anterior  border  bounds  the  obturator  foramen,  the  posterior 
diverging  forms  the  sciatic  arch,  and  shows  the  ischiatic  spine. 

The  external  is  concave,  forming  the  lesser  sciatic  notch. 

The  internal  unites  with  the  opposite  to  form  the  ischial  sym- 
physis. 

The  antero-external  angle  forms  part  of  the  cotyloid  cavity;  the 
antero-internal  unites  with  the  pubis;  the  postero-external  forms 
an  enlargement,  the  tuberosity;  the  posterointernal  unites  with 
the  opposite. 

The  cotyloid  cavity  (or  acetabulum)  is  a  deep  excavation,  at  the 


OSTEOLOGY.  33 

junction  of  the  three  bones,  with  a  narrow  rim  above,  and  incom- 
plete below,  where  it  communicates  with  the  sub-pubic  notch. 
It  receives  the  femoral  head. 

The  obturator  (or  oval)  foramen  is  composed  of  the  pubis  and 
ischium,  and  forms  part  of  the  lower  pelvic  boundary,  when 
closed  in  by  the  external  and  internal  obturator  muscles. 

THE   PELVIS. 

This  cavity  has  an  inlet  bounded  above  by  the  sacrum,  below  by 
the  pubes,  laterally  by  the  ilia. 

It  has  four  diameters,  a  vertical,  from  the  sacrum  to  the  anterior 
pubic  symphysis,  of  8J  inches,  a  horizontal,  between  the  pectineal 
eminences,  of  8T6¥  inches,  and  two  oblique,  from  the  sacro-iliac 
joints  to  the  pectineal  eminences,  of  8T7^  inches. 

It  also  has  an  outlet  through  which  pass  the  rectum  and  genital 
organs,  bounded  above  by  the  summit  of  the  sacrum,  below  by  the 
upper  surface  of  the  ischia,  laterally  by  the  sacro-ischiatic  liga- 
ments. 

It  has  two  diameters,  a  vertical,  of  6^  inches,  from  the  sacrum 
to  the  ischium,  and  a  transverse,  of  7T7¥  inches,  between  the  supra- 
cotyloid  crests. 

The  pelvis  of  the  mare  is  much  more  roomy  than  that  of  the 
male,  being  more  marked  in  its  transverse  diameters. 

THE  THIGH. 

This  consists  of  one  bone,  the  femur. 

THE   FEMUR. 

The  femur  lies  between  the  pelvis  above  and  the  tibia  below, 
having  a  general  .direction  downward  and  forward. 

It  has  a  shaft  and  upper  and  lower  extremities. 

The  shaft  has — 

An  external,  anterior  and  internal  face,  all  smooth  and  convex, 
and  a  posterior,  rough  and  irregular. 

The  posterior  face  shows  in  its  upper  one-third  internally  a 
rough  elevation,  the  lesser  or  internal  trochanter,  a  rough  surface 
for  the  attachment  of  the  pectineus  and  adductor  magnus,  below 
a  deep  groove  and  a  number  of  rough  elevations,  the  supra-condy- 
loid  crest;  in  its  upper  third  rough  lines  and  crests. 


34  EQUINE   ANATOMY. 

The  upper  extremity  shows — 

The  head  articulating  with  the  acetabulum,  forming  two-thirds 
of  a  sphere  and  a  constriction  externally,  the  neck. 

The  great  or  external  trochanter,  outside  and  above,  with  a 
summit,  convexity  and  crest. 

The  digital  or  trochanterian  fossa,  behind  and  below,  receiving 
the  obturator  muscles. 

The  inferior  extremity  is  flattened  laterally  and  shows — 

The  external  and  internal  condyles,  separated  by  a  notch  behind, 
with  depressions  for  the  crucial  ligaments. 

The  trochlea,  a  wide,  smooth  surface  between  the  condyles 
anteriorly,  on  which  the  patella  glides. 

A  fossa  for  muscular  insertion  outside  the  preceding. 

Rough  spots  outside  each  condyle,  for  muscular  and  ligament- 
ous insertion. 
Articulations,  3. 

Os  innominata,  patella  and  tibia. 

THE  LEG. 

This  consists  of  three  bones,  the  tibia,  fibula  (or  peroneus)  and 
patella  (or  knee-pan). 

THE    TIBIA. 

The  tibia  is  a  long  bone.  Its  general  direction  is  downward 
and  backward,  and  has  a  shaft  and  upper  and  lower  extremity. 

The  shaft  has  three  borders  and  three  surfaces. 

The  anterior  border  is  sharp  above,  and  known  as  the  tibial 
crest. 

The  external  border  is  concave  above,  forming  part  of  the  tibial 
arch.     The  internal  border  is  thick. 

The  external  surface  is  concave  above,  convex  below,  giving 
origin  to  the  fleshy  part  of  the  flexor  of  the  metatarsus. 

The  internal  surface  presents  above,  muscular  imprints  for  the 
adductors  and  semi-tendinosus. 

The  posterior  surface  is  divided,  by  an  oblique  line,  into  two 
portions,  the  upper  giving  attachment  to  the  popliteus,  the  lower 
to  the  perforans. 

The  superior  extremity  shows — 

An  anterior  tuberosity,  separated  from  the  external  by  the  groove 


OSTEOLOGY.  35 

for  the  tendon  of  the  -flexor  of  the  metatarsus.    It  has  a  depres- 
sion in  front  for  the  middle  patellar  ligament. 

The  external  tuberosity,  with  a  facet  for  the  fibular  head. 

The  internal  tuberosity,  with  ligamentous  imprints. 

Above,  two  oval  depressions  for  the  condyles  of  the  femur;  the 
external  is  the  wider.  Between  the  two  an  eminence,  the  spine, 
for  attachment  of  ligaments  and  cartilages. 

The  inferior  extremity  shows — 

An  external  tuberosity,  with  a  vertical  fissure  for  the  lateral 
extensor  of  the  phalanges. 

An  internal  tuberosity,  with  an  oblique  channel  for  the  oblique 
flexor  of  phalanges. 

An  articular  surface  for  the  astragalus,  two  antero-posterior 
depressions,  separated  by  a  median  elevation. 
Articulations,  4. 

Femur,  patella,  fibula  and  astragalus. 

THE   FIBULA  OR  PERONEUS. 

The  fibula  is  a  rudimentary  bone  lying  outside  the  tibia  and 
articulating  with  it  alone. 

It  has  a  superior  and  inferior  extremity  and  shaft. 

The  superior  extremity  is  called  the  head,  and  shows  internally 
an  articular  facet  for  the  tibia,  externally  rough  elevations  for 
ligaments. 

The  inferior  extremity  ends  in  a  blunt  point  at  the  end  of  the 
upper  third  of  the  tibia. 

The  shajt  is  thin  and  small,  forming  the  outer  side  of  the  tibial 
arch. 

THE  PATELLA. 

The  patella  is  a  sesamoid  bone,  developed  in  the  tendon  of  the 
triceps  extensor  and  strongly  attached  to  the  tibia  by  three  liga- 
ments. 

It  has  a  superior  face,  rough,  for  attachment  of  the  extensor 
cruris.  An  anterior,  convex,  and  a  posterior,  covered  with  carti- 
lage and  divided  by  a  median  ridge  into  an  external  and  internal 
articular  facet,  the  latter  the  larger,  and  both  articulating  with  the 
femoral  trochlea. 
Articulations,  2. 

Femur  and  tibia. 


36  EQUINE  ANATOMY. 

THE  FOOT. 

This  is  divided  into  the  tarsus,  metatarsus  and  bones  of  the 
digit. 

THE  TARSUS. 

The  tarsus  corresponds  to  the  carpus  of  the  anterior  foot,  and 
consists  of  six  or  seven  segments. 

These  segments  are  divided  into  two  rows:  an  upper  and  lower. 
In  the  former,  in  front,  is  the  astragalus,  behind  the  os  colds;  in 
the  latter,  outside,  is  the  cuboid,  inside,  above,  the  scaphoid,  below 
the  large  and  small  cuneiforms.  There  are  sometimes  three  cunei- 
forms, making  seven  segments. 

THE   ASTRAGALUS. 

The  astragalus  lies  between  the  tibia  above,  the  scaphoid  below, 
and  the  calx  behind. 

It  has  external  and  internal  rough  faces,  a  posterior  with  facets 
for  the  os  calcis,  an  inferior  convex  for  the  articulation  with  the 
scaphoid  and  a  superior  and  anterior  with  two  articular  elevations 
and  a  depression  for  the  tibial  articular  surface. 
Articulations,  4. 

Tibia,  os  calcis,  scaphoid  and  cuboid. 

THE   OS   CALCIS   OR  CALCANEUS. 

The  os  calcis  is  elongated,  lying  behind  the  astragalus,  above 
the  cuboid,  and  forming  the  summit  of  the  tarsus.     It  shows — 

A  convex  outer  surface  and  concave  inner,  forming  the  tarsal 
arch. 

A  concave  anterior  and  thick  posterior  border. 

A  superior  extremity  with  a  rough  spot  for  insertion  of  the  gas- 
trocnemius, a  smooth  surface  on  which  the  tendon  plays,  and 
behind  another  for  the  gliding  of  the  perforatus. 

The  inferior  extremity  shows  articular  facets  for  the  astragalus 
and  cuboid. 

Articulations,  2. 

Astragalus  and  cuboid. 

The  cuboid  is  irregularly  quadrilateral  in  shape,  and  articulates 
with  the  calcaneus,  astragalus,  scaphoid,  middle  and  external 
metatarsals,  and  large  cuneiform. 


ARTHROLOGY.  37 

The  scaphoid  is  boat-shaped,  articulating  with  four;  the  astrag- 
alus above,  cuneiforms  below,  and  the  cuboid  externally. 

The  great  cuneiform  (wedge-shaped),  lies  inside  the  cuboid, 
articulating  with  it,  the  small  cuneiform,  scaphoid,  middle  and 
internal  metatarsals. 

The  small  cuneiform  lies  on  the  inner  side  of  the  tarsus,  articu- 
lating with  the  scaphoid,  large  cuneiform,  middle  and  internal 
metatarsals. 

THE  METATARSUS. 

The  median  is  longer  and  larger  than  that  in  the  anterior  ex- 
tremity. The  external  is  longer  and  thicker  than  the  internal 
which  has  two  facets  above  for  the  tarsus. 

THE  DIGITAL  REGION. 

The  first  phalanx  is  shorter,  the  second  narrower,  the  third 
narrower,  more  V-shaped,  the  sesamoid  smaller,  and  the  navicu- 
lar shorter  and  narrower  than  the  corresponding  bones  of  the 
anterior  foot. 

ARTHROLOGY. 

,  The  articulations  are  divided  into  three  classes: 

1.  Synarthroses  or  immovable  joints. 

2.  Amphiarthroses  or  limited  in  motion. 

3.  Diarthroses,  freely  movable  joints. 

Synarthroses  are  further  divided  into — 

(a)  Schindylesis,  a  bony  plate  received  into  a  groove. 

(b)  Gomphosis,  a  conical  process  in  a  socket. 

(c)  Sutura  or  by  indentation,  which  are  again  divided  into 
sutura  vera  and  sutura  notha. 

(d)  Sutura  vera,  true  sutures. 
Sutura  denlata,  tooth-like  processes. 
S.  serrata  with  saw-like  processes. 

S.  limbosa  with  beveled  margins  and  dentated  processes. 

(e)  Sutura  notha,  false  sutures. 

S.  harmonia  by  opposed  rough  surfaces. 
S.  squamosa  with  overlapping  bony  tables. 

Diarthroses  are  divided  again  into — 
Arthrodial,  or  gliding  joints. 


38  EQUINE   ANATOMY. 

Enarthrodial,  or  ball  and  socket. 
Ginglymus,  or  hinge-like. 

Diarthrosis  rotatoria,  or  a  pivot  which  turns  in  a  cavity. 
Condyloid,  one  or  more  condyles  received  in  oval  excavations. 
Examples. 

S.  dentata. — Intra-parietal  suture. 

S.   serrata. — Inter-frontal  suture. 

S.  limbosa. — Fronto-parietal  suture. 

S.  Juirmonia. — Occipito-temporal  suture. 

S.  squamosa. — Parieto-temporal  suture. 

Amphiarthroses. — Bodies  of  vertebrae,  sacro-iliac  joints. 

Arthrodial. — Carpo-metacarpal  joints. 

Enarthrodial. — Hip  and  shoulder  joints. 

Ginglymus. — Hock  and  humero-radial  joints. 

Diarthrosis  rotatoria. — Atlo-axoid  joint. 

Condyloid. — Temporo-maxillary  and  knee-joints. 

Structures  entering  into  joints  are — 

Articular  lamellae  of  bone,  ligaments,  cartilage,  fibro-cartilage, 
synovial  membrane  and  synovia. 

Movements  of  joints  are — 

Flexion,    extension,    abduction,    adduction,    external   rotation, 
internal  rotation,  circumduction  and  gliding. 
Articulations  of  vertebral  column — 

1.  Common  superior  vertebral  ligament,  lies  above  bodies  of 
vertebrae,  and  attached  to  them  from  the  axis  to  the  sacrum. 

2.  Common  inferior  vertebral  ligament,  lies  below  bodies,  and 
attached  to  them  from  sixth  or  eighth  dorsal  to  sacrum. 

3.  Inter  articular    fibro-cartilage,    between    the    bodies    of    the 
vertebrae,  except  between  atlas  and  axis. 

4.  Capsular,  between  articular  processes. 

5.  Inter-transverse,  between  transverse  processes. 

6.  Inter-lamellar,  between  laminae. 

7.  Inters pinous,  between  spinous  processes. 

8.  Supraspinous,  between  tips  of  spinous  processes. 
Ligamentum  nucha  is  the  continuation  of  the  supra-spinous 

ligament  from  the  first  dorsal  to  the  occiput;  it  supports  the  head. 
In  the  sacral  and  coccygeal  regions  the  articulations  are  more 
or  less  fused  or  rudimentarv. 


ogy.  39 

he  interarticular  fibro-cartilage 

>cess  of  the  last  lumbar  articu- 

crum. 

articulate  between  their  trans- 


are — 

otion,  free  in  the  cervical  but 

TCULATION. 

j  of  axis  to  corresponding  de- 


ior  arch  of  atlas. 

Inferior  atlo-axoid,  below  bodies. 

Capsular  ligaments  (two),  between  articular  processes. 

Action. 

Lateral  rotation. 

OCCIPITO- ATLOID . 

Ligaments. 

Two  capsular. 

Two  lateral,  from  transverse  process  to  occiput. 

Action. 

(Condyloid,)  extension,  flexion  and  lateral  inclination. 

TEMPORO-MAXILLARY. 

(Double  condyloid  joint.) 
Ligaments. 

Capsular,  from  margins  of  glenoid  cavity  to  neck  of  condyle 
of  inferior  maxilla. 

Interarticular  fibro-cartilage  moulded  on  condyle. 

Two  synovial  membranes,  one  above,  one  below  cartilage. 

Action. 

Depression,  elevation,  lateral  motion  and  gliding. 


40  EQUINE   ANATOMY. 

HYOID. 

Two  elastic  cartilages,  between  styloid  bone  and  temporal. 
Two  capsular  ligaments,  between  body  and  lesser  cornua. 

Motion. 

Amphiarthrodial. 

THORAX. 

COSTO-VERTEBRAL. 

Two  convex  facets  on  head  of  ribs  and  two  depressions  in 
vertebrae,  in  front  and  behind,  also  in  the  intervertebral  substance. 

Ligaments. 

Inter  articular,  from  head  of  rib  to  intervertebral  disk,  none  in 
first,  and  sometimes  not  in  second  articulation. 

Inferior  (stellate),  of  three  fasciculi,  running  to  vertebrae  in  front 
and  behind  and  intervertebral  substance. 

Two  capsular  ligaments,  one  in  front  and  one  behind  the  inter- 
articular  ligament. 

COSTO-TRANS  VERSE . 

Between  facet  on  tuberosity  of  rib  and  dorsal  transverse  proc- 
esses. 

Anterior  costo-transverse  or  interosseous. 
Posterior  costo-transverse. 
One  synovial  membrane. 

CHONDRO-STERNAL. 

Eight  upper  ribs,  with  sternum,  by  cartilages. 

Superior  chondro-sternal. 

Inferior  chondro-sternal. 

The  articulations  of  the  first  two  ribs  run  into  each  other. 

CHONDRO-COSTAL. 

Implantation  of  a  cartilage,  on  the  one  in  front,  by  means  of 
diarthrodial  facets. 

Their  movements  are  obscure. 


ARTHROLOGY.  4 I 

ANTERIOR  LIMB. 

SCAPULOHUMERAL. 

Enarthrodial  joint,  between  the  head  of  humerus  and  glenoid 
cavity  of  scapula. 
Ligaments. 

A  rudimentary  glenoid  ligament,  deepening  the  cavity. 

Capsular  ligament,  from  margins  of  cavity  to  neck  of  humerus. 
Two  supporting  fasciculi  from  coracoid  process  to  head  of  humerus. 

The  muscles  in  relation  to  joint  are — 

i.  In  front,  coraco-radial. 

2.  Behind,  large  extensor  of  forearm  and  teres  minor. 

3.  Outside,  short  abductor  of  arm  and  postea  spinatus. 

4.  Inside,  subscapularis. 
Action. 

Abduction,    adduction,    flexion,    extension,    rotation   and   cir- 
cumduction. 

HUMERORADIAL. 

Ginglymus,  between  inferior  extremity  of  humerus  and  upper 
extremity  of  ulna  and  radius. 
Ligaments. 

Anterior,  from  humerus  above  articular  surface  to  anterior  part 
of  radius. 

External  lateral,  from  cavity  outside  of  humerus  to  external 
portion  of  radius. 

Internal  lateral,  inner  tuberosity  of  inferior  extremity  of  humerus, 
to  radial  tuberosity  and  to  interosseous  fibres. 
Action. 

Flexion  and  extension. 

RADIO-ULNAR. 

Two  facets  and  rough  surfaces  on  each  bone. 
Ligaments. 

Two  interr osseous,  the  lower  always  ossifies,  the  upper  rarely. 

External  peripheral  band. 

Internal  peripheral  band. 
Action. 

Very  little  in  youth,  none  when  consolidated. 
4 


42 


EQUINE   ANATOMY. 
Fig.  2. 


SCAPULOHUMERAL  AND   HUMERORADIAL   ARTICULATIONS,   WITH   THE  MUSCLES  SUR- 
ROUNDING  THEM    (EXTERNAL   FACE). 

i,  Scapulo-humeral  capsular  ligament;  2,  Short  abductor  muscle  of  the  arm;  3,  Its 
insertion  in  the  humerus;  4,  Insertion  of  the  subspinous  muscle  on  the  crest  of  the 
great  tuberosity;  s,  Coraco-radial  muscle;  6,  Its  tendon  of  origin  attached  to  the 
coracoid  process;  7,  Its  radial  insertion  confounded  with  the  anterior  ligament 
of  the  ulnar  articulation;  8,  8,  External  lateral  ligament  of  that  articulation;  9, 
Anterior  ligament;  10,  Anconeus,  or  small  extensor  of  the  forearm;  u,  Origin  of 
the  external  flexor  muscle  of  the  metacarpus;  12,  Short  flexor  muscle  of  the  fore- 
arm.—a,  Tuberosity  of  the  scapular  spine.— b,  Superspinous  fossa.— c,  Subspinous 
fossa.— D,  Convexity  of  the  small  trochanter.— e,  Summit  of  the  trochanter. 


ARTHROLOGY.  43 

RADIO-CARPAL. 

Lower  articular  surface,  of  radius  with  four  upper  carpal  bones. 
Ligaments. 

Internal,  from  radius  to  fourth  bone. 

Superficial   external,   radius  to   supercarpal   bone. 

Deep  external,  radius  to  second  bone  and  interosseous  ligament. 
Action. 

Imperfect  ginglymus. 

CARPUS. 

First  row  with  each  other. 

Three  anterior  and  three  interosseous  running  in  front  of  and 
between  bones. 

Second  row  with  each  other. 

Two  anterior  and  two  interosseous. 

First  and  second  rows  with  each  other. 
Ligaments. 

External  posterior,  from  first  of  upper  to  second  bone  of  lower 
row. 

Internal  posterior,  from  internal  bone  of  upper  row  to  second 
and  third  of  metacarpal  row. 

External,  from  supercarpal  to  first  bone  of  second  row  and 
head  of  external  metacarpal. 
Action. 

Imperfect  ginglymus. 

CARPO-METACARPAL. 

Between  three  lower  carpus  and  three  metacarpus,  forming  a 
planiform  diarthrosis. 
Ligaments. 

Two  anterior,  one  between  second  bone  and  principal  meta- 
carpal; the  other  from  the  first  to  external  metacarpal. 

Two  interosseous,  from  articulations  between  metacarpus  to  in- 
terosseous ligaments  of  second  row. 

COMMON  CARPAL  LIGAMENTS. 

i.  Anterior,  from  radius  to  principal  metacarpal. 
2.  Posterior,  posterior  part  of   radial   surface  to  carpus  and 
principal  metacarpal. 


44  EQUINE   ANATCfMY. 

3.  External  lateral,  from  outer  side  of  radius  to  first  bones  of 
upper  and  lower  rows  and  outer  metacarpal  bone. 

4.  Internal  lateral,  from  inner  side  of  the  radius  to  principal 
and  inner  metacarpal  as  well  as  into  carpus. 

METACARPOPHALANGEAL. 

Ginglymus  joint  between  end  of   metacarpal  bone  and  first 
phalanx,  with  the  two  upper  sesamoids. 
Ligaments. 

Inter-sesamoid,  between  two  sesamoids. 

Lateral  sesamoid,  between  sides  of  sesamoids  and  upper  extrem- 
ity of  first  phalanx. 

Inferior  sesamoid,  of  three  fasciculi,  from  posterior  surface  of 
first  phalanx  to  sesamoids. 

External  and  internal  lateral,  from  metacarpal  to  sides  of  first 
phalanx. 

Anterior,  between  anterior  surfaces  of  both  bones. 

Posterior  or  suspensory  ligament  of  the  fetlock,  from  first  and 
second  bone  of  inferior  carpal  row  and  posterior  face  of  principal 
metacarpal  to  top  of  sesamoids,  divides  into  two  fasciculi  which 
pass  forward  and  are  inserted  into  the  anterior  extensor  of  the 
phalanges. 
Movements. 

Flexion  and  extension. 

FIRST   INTER-PHALANGEAL  ARTICULATION. 

Imperfect  ginglymus  between  first  and  second  phalanges. 
Ligaments. 

Two  lateral  ligaments  between  sides  of  bones. 

One  posterior  ligament  or  glenoidal  fibro-cartilage  attached  to 
the  first  and  second  phalanges  by  six  bands.  It  increases  the  ar- 
ticular surface  below  and  forms  a  sheath  for  the  passage  of  the 
perjorans  tendon,  being  in  relation  to  the  perjoratus  at  its  side. 
Movements. 

Flexion,  extension  and  some  lateral  motion. 

SECOND   INTER-PHALANGEAL  ARTICULATION. 

Imperfect  ginglymus,  between  second  and  third  phalanges. 
Ligaments. 

Interosseous,  between  navicular  and  pedal  bones. 


ARTHROLOGY.  45 

Two  anterior  lateral,  from  anterior  surfaces. 
Two  posterior  lateral,  from  anterior  surfaces. 
Movements. 

Same  as  preceding. 

POSTERIOR  EXTREMITY. 

SACROILIAC. 

An  amphiarthrosis,  between  auricular  surface  of  sacrum  and 
side  of  ilium. 

Ligaments. 

Sacro-iliac,  about  margins  of  articulation. 

Superior  ilio-sacral,  from  internal  angle  of  ilium  to  sacral  spine. 

Inferior  ilio-sacral,  with  preceding  and  inserted  into  sides  of 
sacrum. 
Movements. 

Slight  gliding. 

Sacro-iliac  ligament,  from  sides  of  sacrum  by  its  superior  bor- 
der into  super-cotyloid  crest  and  ischial  border  by  its  inferior 
border,  forming,  with  the  lesser  sciatic  notch,  the  opening  by  which 
the  internal  obturator  and  pyramidal  muscles  leave  the  pelvis. 

An  anterior  border  forms  the  greater  sciatic  foramen  with  the 
notch,  and  through  it  pass  the  gluteal  and  sciatic  vessels  and 
nerves. 

A  posterior  border  which  embraces  the  semi-membranosus 
muscle. 

ISCHIO-PUBIC   SYMPHYSIS. 

In  young  animals  is  a  true  amphiarthrosis. 
In  adult  life  bones  are  fused  together. 

COXO-FEMORAL   OR  HIP   JOINT. 

An  enarthrodia  between  the  cotyloid  cavity  and  the  head  of  the 
femur. 
Ligaments. 

Capsular,  from  margins  of  cotyloid  cavity  to  neck  of  femur. 

'Transverse,  converting  notch  into  a  foramen. 

Cotyloid,  deepening  the  cavity. 


46 


EQUINE   ANATOMY, 


Coxo-jemoral  (ligamentum  teres)  from  bottom  of  cotyloid 
cavity  to  a  depression  in  head  of  femur. 

Pubo-femoral,  from  inferior  face  of  pelvis,  to  be  inserted  with 
the  preceding. 

Synovial  membrane,  very  extensive. 

Fig.  3. 


SACROILIAC   AND   COXO-FEMORAL   ARTICULATIONS,    WITH    THE    SMALL   DEEP 
MUSCLES    SURROUNDING   THE    LATTER. 

i,  Sacro-iliac  ligament;  2,  Sacro-ischiatic  ligament;  3,  Great  ischiatic  notch;  4,  Ante- 
rior portion  of  the  capsular  ligament  of  the  coxo-femoral  articulation;  5,  Internal 
band  of  cotyloid  ligament;  6,  Coxo-femoral  ligament;  7,  Pubio-femoral  ligament; 
8,  Its  insertion  into  the  femur;  9,  Small  gluteal  muscle;  10,  Origin  of  the  straight 
anterior  muscle  of  the  thigh  (rectus);  11,  Anterior  thin  muscle  (rectus  parvus); 
12,  Pyramidal  muscle  of  the  pelvis;  13,  External  obturator  muscle;  14,  Square 
crural  muscle  (quadratus  femoris);  15,  Inferior  sacro-coccygeal  muscle. 


Muscles  in  relation  to  joint; — 
In  front. — Gracilis  and  rectus. 
Behind. — Gemelli,  internal  obturator  and  pyramidalis. 


ARTHROLOGY.  47 

Below. — Ext.  obturator. 
Above. — Small  gluteal. 
Action. 

Same  as  shoulder. 

FEMORO-TIBIAL  ARTICULATION. 

A  condyloid  joint  between  the  femur  above,  tibia  below   and 
patella  in  front. 

Fig.  4. 


No.  2.  External  face;  the  external  condyle  of  the  femur  and  the  meniscus  have  been 
removed  to  show  the  crucial  ligaments. — i,  Anterior  crucial  ligament;  2,  Posterior 
ditto;  3,  Fibular  insertion  of  the  external  lateral  ligament;  4,  Anterior  patellar 
ligaments.— a,  Internal  meniscus;  «,  Anterior  insertion  of  the  external  meniscus; 
c,  Passage  for  the  tendinous  cord  common  to  the  flexor  of  the  metatarsus  and  the 
anterior  extensor  of  the  phalanges;  d,  Anterior  and  superior  tuberosity  of  the 
tibia;  e,  Tibial  crest. 

Ligaments. 

Anterior  or  ligamentum  patellce  of  three  strong  fasciculi  from 
patella  to  the  anterior  surface  of  the  tibia. 

Ante-patellar  aponeurosis,  an  expansion  of  the  fascia  lata  bind- 
ing patella  to  the  femur  by  two  lateral  fasciculi. 

External  lateral,  from  external  condyle  to  head  of  fibula. 

Internal  lateral,  from  internal  condyle  to  inner  tibial  tuberosity. 


48  EQUINE  ANATOMY. 

Posterior,  from  posterior  face  of  femur  to  tibia.    In  relation  to 
external  gastrocnemius  and  popliteal  artery. 
Crucial. 

(a)  Anterior  or  external  from  front  of  tibial  spine  to  inner  side 
of  external  condyle. 

(b)  Posterior  or  internal,  in  opposite  direction. 

Inter  articular  fibro-cartilages   (or  menisci),   (a)  right    and  (b) 
lejt  attached  to  tibial  spine,  and  by  fasciculi  to  femur  and  tibia. 
Synovial  membrane. 

(a)  Middle  portion  under  patella. 

(b)  Lateral  portions  under  lateral  ligaments. 
Action. 

Flexion,  extension  and  rotation  on  menisci. 

TIBIOFIBULAR  ARTICULATION. 

A  planijorm  diarthrosis,  between  tibia  and  fibula. 
Ligaments. 

Two  lateral  fasciculi,  from  sides  of  fibula  to  tibia. 

Interosseous,  between  two  bones,  leaving  a  space  called  tibio- 
fibular arch. 
Action. 

Limited. 

HOCK   OR  TARSAL  ARTICULATION. 

Tibio-tarsal. 

A  ginglymus,  between  lower  end  of  tibia  and  astragalus. 
Ligaments. 

Anterior. — From  front  of  tibia  to  astragalus,  scaphoid,  great 
cuneiform  bones  and  astragalo-metatarsal  ligament. 

Internal  lateral. 

(a)  Superficial  fasciculus,  from  inner  extremity  of  tibia  to  sides 
of  tarsus  and  metatarsus. 

(b)  Middle  fasciculus. 

Tibial  tuberosity  to  astragalus  and  calx. 

(c)  Deep  fasciculus. 
From  tibia  to  astragalus. 
External  lateral. 

(a)  Superficial  portion,  from  tibia  to  sides  of  tarsus  and  meta- 
tarsus. 


ARTHROLOGY.  49 

(b)  Deep  portion,  from  tibia  to  astragalus  and  calx. 
Action. 

Flexion  and  extension. 
Calcaneo-astragaloid. 

A  compound  diarthrodia  between  three  or  four  facets  on  astrag- 
alus, with  same  on  calx. 

Ligaments. 

Superior,  external  lateral,  internal  lateral  'and  interosseous, 
running  from  one  bone  to  another,  as  their  names  imply. 

Action. — Very  limited. 

Second  row  of  tarsus  with  each  other.  Between  scaphoid,  cuboid 
and  two  cuneiforms. 

Ligaments.  • 

Two  anterior,  the  cuboido-cunean  and  cuboido-scaphoid  and 
two  corresponding  interosseous. 

An  interosseous  scaphoid-cunean  and  inter-cunean. 

Action. — Very  limited. 

Two  rows  of  tarsus  with  each  other. 
Ligaments. 

Two  lateral  ligaments  of  tibio-tarsal  joint. 

Calcaneo-metatarsal,  from  posterior  border  of  calx  to  cuboid 
and  head  of  external  metatarsal. 

Astragalo-metatarsal,  from  inner  side  of  astragalus  to  scaphoid, 
great  cuneiform  and  middle  metatarsal. 

Posterior  tarso-metatarsal  from  all  of  tarsus  to  top  of  metatarsus. 

One  interosseous,  between  four  bones. 

Action. — Very  limited. 
Tarso-metatarsal. 

Between  cuboid  and  cuneiform  above,  and  metatarsal  below. 
Ligaments. 

Those  previously  described  and  one  strong  interosseous. 

Synovial  sacs  of  tarsus. 

1 .  Membrane  of  tibio-tarsal  articulation,  communicates  in 
front  with  that  between  the  two  rows,  and  behind  with  the  superior 
articulation  of  astragalus  with  calx. 


50  EQUINE  ANATOMY. 

2.  One  for  articulation,  between  scaphoid  and  great  cuneiform, 
and  also  to  the  cuboido-scaphoid  and  posterior  cuboido-cunean. 

3.  That  between  two  rows,  which  has  communications  as  above, 
and  with  anterior  cuboido-scaphoid  joint. 

4.  That  of  tarso-metatarsal  articulation  which  ascends  into  an- 
terior cuboido-cunean  joint  between  cuneiform  and  down  into 
inter-metatarsal  articulation. 

MYOLOGY. 
THE  MUSCLES. 

The  muscles  are  the  active  portions  of  the  locomotory  apparatus, 
and  form  one-half  of  the  body's  weight. 

They  are  divided  into  striated  or  striped  and  unstraited  or  un- 
striped.     The  former  are  voluntary  and  the  later  involuntary. 

The  striped  muscles  consist  of  fibres  divided  into  fibrillce,  the 
whole  being  surrounded  by  a  membrane,  the  perimysium.  The 
fibrillar  are  composed  of  small  portions,  the  sarcous  elements,  at- 
tached to  each  other  end  to  end.  Between  the  fibrillar  is  more  or 
less  interstitial  substance. 

The  unstriped  muscles  are  found  in  the  viscera  as  the  intestine 
and  consist  of  fusiform  cells,  each  with  a  distinct  nucleus  and 
bound  together  by  connective  tissue. 

Appendages  of  Muscles. 

These  are  tendons,  jascia  and  aponeuroses. 

Tendons  are  round,  or  flattened,  white  cords  at  the  termination 
of  muscles,  composed  of  condensed  white  fibrous  tissue. 

Aponeuroses  are  flattened  bands  connected  with,  or  the  termi- 
nations of,  the  broad  muscles,  and  composed  of  white  fibrous 
tissue. 

Fascia  are  strong  processes  of  the  same  structure,  forming 
sheaths  and  coverings  for  the  muscles. 

Bursa  are  thin  bags  filled  with  mucous  or  serous  fluid,  and 
placed  on  bony  points  over  which  muscles  glide.  Their  office  is 
to  prevent  friction. 

Sheaths  of  tendons  are  composed  of  fibrous  tissue,  forming  de- 
pressions or  compartments  in  which  tendons  glide.  When  com- 
plete they  are  called  vaginal.  They  may  be  lined  with  synovial 
membrane. 


MYOLOGY.  5 1 

MUSCLES  OF  FACE. 

ORBICULARIS   ORIS. 

Origin. — No   bone   attachment;   confounded  with  buccinator 
and  other  muscles  in  vicinity. 
Insertion. — About  oral  orifice. 
Action — To  close  oral  orifice. 
Nerve. — Facial. 

BUCCINATOR. 

Origin. — Maxillary  tuberosity,  above  posterior  three  molar 
teeth  of  superior  maxilla  and  from  interior  maxilla,  behind  last 
molar. 

Insertion. — Into  orbicularis. 

Action. — Compresses  cheeks. 

Nerve. — Buccal,  from  fifth. 

ZYGOMATICO-LABIALIS. 

Origin. — From  outer  surface  of  masseteric  fascia. 
Insertion. — On  surface  of  buccinator. 
Action. — Retraction  of  lips. 
Nerve. — Facial. 

LACHRYMO-LABIAL. 

Origin. — Outer  surface  of  lachrymal  and  malar  bones. 
Insertion. — Into  buccinator  fascia. 
Action. — To  corrugate  skin  of  lower  lid. 
Nerve. — Facial. 

SUPER-NASO-LABIALIS. 

(Levator  labii  superioris  et  aloeque  nasi  of  man.) 

Origin. — Frontal  and  nasal  bones. 

Insertion. — Anterior  division  into  external  wing  of  nose  and 
buccinator,  posterior  into  angle  of  lips;  between  divisions  passes 
the  super-maxillo-labialis  magnus. 

Action. — Raises  wing  of  nose  and  upper  lip. 

Nerve. — Facial. 

SUPER-MAXILLO-LABIALIS. 

Origin. — Outer  surface  of  super-maxillary  and  malar  bones. 
Insertion. — With  opposite  into  fascia  of  upper  lip. 
Action. — Raises  upper  lip,  or  singly  carries  it  to  one  side. 
Nerve. — Facial. 


52 


EQUINE  ANATOMY. 
SUPER-MAXILLO-NASALIS   MAGNUS. 


Origin. — Below  ridge  on  superior  maxilla. 
Insertion. — Skin  of  external  wing  of  nostril. 
Action. — Dilates  anterior  nares. 
Nerve. — Facial. 


SUPERFICIAL   MUSCLES    OF  THE    FACE   AND   HEAD. 

Temporo-auricularis  externus,  or  attollens  maximus;  2,  Levator  palpebral,  or  cor- 
rugator  supercilii;  3,  Temporo-auricularis  internus,  or  attollens  posterior;  4,  5, 
Zygomatico-auricularis,  or  attollens  anterior;  6,  Orbicularis  palpebrarum;  7, 
Parotido-auricularis,  or  deprimens  aurem;  8,  Parotid  gland;  9,  Temporal,  or  sub- 
zygomatic  vein;  10,  Ditto,  artery;  11,  12,  Superior  and  inferior  maxillary  nerves; 
13,  Fascia  of  the  masseter  muscle;  14,  Nasal  bones;  15,  Super-naso  labialis,  or 
levator  labii  superioris  alseque  nasi;  16,  Super-maxillo-labialis,  or  nasalis  longus 
labii  superioris;  17,  External  maxillary  or  facial  artery;  18,  Facial  vein;  19,  Super- 
maxillo-nasalis  magnus,  or  dilator  naris  lateralis;  20,  Superior  maxillary  nerve; 
31,  Zygomatico-labialis.or  zygomaticus;  22,  Parotid,  or  Steno's  duct;  23,  Masseter; 
24,  Alveolo-labialis,  or  buccinator;  25,  Super-maxillo-nasalis  parvus,  or  nasalis 
brevis  labii  superioris;  27,  Labialis,  or  orbicularis  oris;  28,  Maxillo-labialis,  or 
depressor  labii  inferioris;  29,  Mento-labialis,  or  levator  menti. 


SUPER-MAXILLO-NASALIS   MINOR. 

Origin. — External  process  of  pre-maxilla  and  superior  maxilla. 
Insertion. — Skin  and  cartilage  of  nostril. 
Action. — Dilatation  of  nostril. 
Nerve. — Facial. 


MYOLOGY.  53 

| 

TRANSVERSALIS   NASI. 

Runs  from  one  internal  ala  of  nose  to  the  other. 
Action. — To  dilate  nostrils. 
Nerve. — Facial. 

ANTERIOR  INTERMEDIATE. 

Origin. — Facial  surface  of  pre-maxilla  above  incisors. 
Insertion. — With  maxillo-nasalis  minor  into  inferior  turbinated 
bone. 

Action. — Dilation  of  anterior  nasal  entrance. 
Nerve. — Facial. 

MAXILLO-LABIALIS. 

Origin. — Inferior  maxilla  behind  last  molar. 
Insertion. — Skin  of  lower  lip. 

Action. — Depresses  lower  lip,  or  singly  moves  it  laterally. 
Nerve — Facial. 

POSTERIOR  INTERMEDIATE. 

Origin. — Outer  surface  of  inferior  maxilla  beneath  incisors. 
Insertion. — Into  fibers  of  orbicularis  oris. 
Action. — Elevates  lower  lip. 
Nerve. — Facial. 

MASSETER. 

Origin. — Zygomatic  process  of  temporal. 
Insertion. — Outer  surface  of  ramus  of  jaw. 
Action. — Elevator  of  jaw. 
Nerve. — Inferior  maxillary  of  fifth. 

TEMPORAL. 

Origin. — From  temporal  fossa,  temporal  fascia  and  outer  border 
of  orbit. 

Insertion. — Coronoid  process  and  ramus  of  inferior  maxilla. 
Nerve. — Buccal  branch  of  fifth. 

EXTERNAL  PTERYGOID. 

Origin. — Under  surface  of  sphenoid  and  pterygoid  process. 
Insertion. — Neck  of  condyle  of  maxilla. 

Action. — To  pull  inferior  maxilla  forward,  alone  to  cause  lateral 
motion,  as  in  grinding  food. 
Nerve. — Buccal  branch  of  fifth. 


54  EQUINE   ANATOMY. 

INTERNAL   PTERYGOID. 

Origin. — Palatine   crest   and   pterygoid   process. 
Insertion. — In  hollow  of  maxillary  ramus. 
Action. — Elevates  and  moves  jaw  laterally. 
Nerve. — Inferior  maxillary  of  fifth. 

DIGASTRIC. 

Origin. — Posterior  belly  from  styloid  process  of  occipital  bone; 
tendon  passes  through  fibrous  ring  of  insertion  of  stylo-hyoideus 
into  hyoid. 

Insertion. — Into  posterior  border  and  internal  face  of  inferior 
maxilla. 

Action. — Raises  hyoid  bone  or  depresses  lower  jaw. 

Nerve. — Facial. 

MYLO-HYOID. 

Origin. — Mylo-hyoid  ridge  of  inferior  maxilla. 
Insertion. — Body  of  hyoid  and  anterior  appendix  and  median 
raphe  between  two  muscles. 

Action. — Same  as  above  and  also  elevates  tongue. 
Nerve. — Inferior  maxillary  of  fifth. 

GENIO-HYOID. 

Origin. — Genial  surface  of  inferior  maxilla. 
Insertion. — Extremity  of  hyoideal  appendix. 
Action. — Draws  hyoid  forward  and  upward. 
Nerve. — Hypoglossal. 

STYLO-HYOID. 

Origin. — Superior  angle  of  styloid  bone. 

Insertion. — Base  of  hyoideal  cornua. 

Action. — Antagonizes  former;  carries  hyoid  up  and  back. 

Nerve. — Facial. 

KERATO-HYOID. 

Origin. — Posterior  border  of  styloid  cornu  and  inferior  ex- 
tremity of  hyoid  bone. 

Insertion. — Superior  border  of  thyroid  cornua. 
Action. — Approximates  two  cornua. 
Nerve. — Hypoglossal . 


MYOLOGY. 


55 


"  OCCIPITO-STYLOLD. 

Origin. — Styloid  process  of  occipital. 

Insertion. — Horizontal  portion  of  posterior  border  of  the  styloid 
bone. 

Action. — Depresses  inferior  extremity  of  hyoid. 
Nerve. — Facial. 

TRANSVERSUS  HYOIDEI. 

Runs  between  superior  extremities  of  styloid  cornua. 
Action. — Approximates  styloid  cornua. 
Nerve. — Hypoglossal. 

TONGUE. 

STYLO-GLOSSUS. 

Origin. — Outer  surface  of  lower  extremity  of  styloid  bone. 
Insertion. — Side  and  tip  of  tongue. 

Action. — Pulls  tongue  up  and  backward  or  to  one  side  alone. 
Nerve . — Hypoglossal . 

HYO-GLOSSUS   MAXIMUS. 

Origin. — Side  of  appendix,  body  and  great  cornua  of  hyoid. 

Insertion. — Lateral  borders  of  tongue. 

Action. — Retracts  tongue  and  depresses  its  base. 

GENIO-GLOSSUS. 

Origin. — Posterior  surface  of  body  of  lower  jaw,  near  symphysis. 

Insertion. — Under  surface  of  tongue. 

Action. — Pulls  tongue  forward  or  depresses  it. 

Nerve. — Hypoglossal. 

HYO-GLOSSUS  MINIMUS. 

Origin. — Body  of  hyoid  near  small  branch. 

Insertion. — Into  base  of  tongue. 

Action. — Contracts  and  retracts  tongue. 

PALATE. 

PALATO-GLOSSUS. 

Origin. — From  lateral  wall  of  pharynx. 
Insertion. — Into  side  of  tongue  between  hyo-  and  genio-glossi. 
Action. — Elevates  tongue. 

Nerve. — Superior    maxillary    division   of   fifth   and   Meckel's 
ganglion. 


56  EQUINE   ANATOMY. 

PALATO-PHARYNGEUS . 

Origin. — From  soft  palate. 

Insertion. — Side  of  pharynx  and  superior  border  of  thyroid 
cartilage. 

Action. — Makes  tense  and  elevates  free  border  of  palate. 

Nerve. — Superior  maxillary  division  of  fifth  and  Meckel's 
ganglion. 

PALATO-STAPHYLEUS. 

Origin. — Uvular  aponeurosis  with  opposite. 
Insertion. — Into  free  border  of  soft  palate. 
Action. — Pulls  palate  upward  and  forward. 
Nerve. — Posterior  palatine. 

PERI-STAPHYLEUS   EXTERNUS    (TENSOR   PALATl) 

Origin. — Styloid  process  of  temporal. 

Insertion. — Winds    around    pterygoid    trochlea,    changes    its 
direction  and  spreads  out  into  soft  palate. 
Action. — Tensor  of  soft  palate. 
Nerve. — Posterior  palatine. 

PERI-STAPHYLEUS   INTERNUS    (LEVATOR  PALATl). 

Origin. — With  preceding. 

Insertion. — Into  palato-pharyngeus  and  soft  palate. 

Action. — Elevator  of  soft  palate. 

Nerve. — Posterior  palatine. 

PHARYNX. 

palato-pharyngeus. — See  above. 

PTERYGO-PHARYNGEUS    (SUPERIOR   CONSTRICTOR). 

Origin. — Pterygoid  process. 

Insertion. — Into  median  raphe,  with  opposite,  and  hyoid  and 
thyroid  cartilage. 

Action. — Constricts  pharynx  and  raises  larynx. 

HYO-PHARYNGEUS    (FIRST   MIDDLE   CONSTRICTOR). 

Origin. — Cornua  of  hyoid. 
Insertion. — Median  raphe. 


MYOLOGY.  57 

THYRO-PHARYNGEUS    (SECOND   MIDDLE  CONSTRICTOR). 

Origin. — External  surface  of  thyroid  cartilage. 
Insertion. — Median  raphe. 

CRICO-PHARYNGEUS    (INFERIOR   CONSTRICTOR). 

Origin. — Superficial  face  of  cricoid. 

Insertion. — Median  raphe. 

Action. — With  three  above,  as  constrictors  of  pharynx. 

Nerves. — Glossopharyngeal,    pneumogastric,     sympathetic. 

STYLO-PHARYNGEUS . 

Origin. — Great  throideal  cornua. 
Insertion. — Sides  of  pharynx. 
Action. — Elevates  and  dilates  pharynx. 
Nerves. — §ame  as  preceding. 

TRUNK. 

FLESHY   PANNICULUS. 

Origin. — From  flank  to  posterior  border  of  olecranian  mass  of 
muscles  and  pectoralis  major. 

Insertion. — One  layer  to  anterior  limb  and  one  to  small  tro- 
chanter. 

Nerve. — Subcutaneous  thoracic. 

CERVICAL  REGION. — RHOMBOIDEUS. 

Origin. — First,  fourth  or  fifth  division  vertebrae  by  spinous 
processes. 

Insertion. — Scapular  cartilage. 

Action. — Draws  shoulder  upward  and  forward. 

Nerve. — Sixth  cervical. 

LEVATOR  ANGULI  SCAPULA. 

Origin. — Transverse  processes  of  last  five  cervical  vertebrae. 
Insertion. — Anterior  triangular  surface  in  inner  face  of  scapula. 
Action. — Draws  scapula  forward  and  upward.     If  scapula  is 
fixed,  inclines  neck  to  side. 
Nerve. — Sixth  cervical. 

SPLENIUS. 

Origin. — To  lip  of  cervical  ligament  and  first  dorsal  vertebrae. 

Insertion. — Into  mastoid  crest  with  small  complexus,  transverse 

processes  of  atlas  and  third,  fourth  and  fifth  cervical  vertebrae. 

5 


58  EQUINE   ANATOMY. 

Action. — Extends  head  and  neck  or  draws  them  to  side. 
Nerve. — Superficial  cervical. 

GREAT   COMPLEXUS. 

Origin,  Anterior  Portion. — Transverse  processes  of  first  and 
second  dorsal  vertebrae,  and  articular  tubercles  of  cervical  vertebrae. 

Posterior  Portion. — From  spinous  process  of  first  dorsal,  and 
transverse  process  of  first  four  or  five  dorsal  vertebrae. 

Insertion. — Occipital  tuberosity. 

Action. — Extensor  of  head. 

Nerve. — Deep  cervical. 

SMALL  COMPLEXUS. 

Origin. — Same  as  anterior  portion  of  former. 
Insertion. — Mastoid  process  of  temporal. 
Action. — Extends  head  and  inclines  it  to  one  side. 
Nerve. — Deep  cervical. 

TRANSVERSE   SPINOUS   OF   NECK. 

Origin. — To  five  last  articular  tubercles  of  cervical  spine. 
Insertion. — Second,  third,  fourth,  fifth  and  sixth  cervical  spinous 
processes. 

Action. — Extensor  and  flexor  of  cervical  region. 
Nerve. — Deep  cervical. 

INTER-TRANSVERSE   OF   NECK. 

Origin. — Six   short   muscles  between  transverse  processes  of 
cervical  spine,  except  between  first  and  second. 
Action. — Incline  neck  to  same  side. 
Nerve. — Superficial  cervical. 

GREAT   OBLIQUE   OF   HEAD. 

Origin. — Spinous  process  of  axis. 
Insertion. — Transverse  process  of  atlas. 
Action. — Rotates  atlas  on  odontoid  process. 
Nerve. — Second  cervical. 

SMALL  OBLIQUE. 

Origin. — Transverse  process  of  atlas. 

Insertion. — Styloid  process,  external  surface  of  occipital  and 
mastoid  crest. 


MYOLOGY.  59 

Action. — Inclines  head  on  atlas. 
Nerve. — First  cervical. 

POSTERIOR   GREAT   STRAIGHT   OF   HEAD. 

Origin. — Spinous  process  of  axis. 
Insertion. — To  occipital  behind  complexus. 
Action. — Extends  head. 
Nerve. — Deep  cervical. 

POSTERIOR   SMALL   STRAIGHT   OF  HEAD. 

Origin. — From  superior  face  of  atlas. 
Insertion. — Below  preceding,  on  occipital. 
Action. — Same  as  preceding. 
Nerve. — Deep  cervical. 

INFERIOR  CERVICAL  REGION. — SUBCUTANEOUS   OF   NECK. 

Origin. — Anterior  prolongation  of  sternum  and  muscles  of 
chest. 

Insertion. — Skin  of  neck — raphe — muscles  of  face,  and  zygo- 
matic crest. 

Action. — Braces  muscles  and  pulls   mouth   backward. 

Nerve. — Facial. 

MASTOIDO-HUMERALIS. 

Origin;  Anterior  Portion. — Mastoid  process  and  crest. 
Insertion. — Furrow  of  torsion  of  humerus  below  deltoid  imprint. 
Origin;  Posterior  Portion. — Transverse  processes  of  first  four 
cervical  vertebrae. 

Insertion. — With  first  portion. 

Action. — Carries  limb  forward  or  inclines  head  to  side. 

Nerve. — Spinal  accessory. 

STERNO-MAXILLARIS. 

Origin. — Cariniform  process  of  sternum. 
Insertion. — Posterior  border  of  inferior  maxilla. 
Action. — Flexes  head  or  turns  it  to  one  side. 
Nerve. — Spinal  accessory. 

STERNO-HYOID. 

Origin. — Cariniform  cartilage  of  sternum. 
Insertion. — Inferior  surface  of  body  of  hyoid. 


6o 


EQUINE   ANATOMY. 


Action. — Depresses  hyoid  and  larynx. 
Nerve. — First  cervical. 

STERNOTHYROID. 

Origin. — As  preceding. 

Insertion. — Posterior  border  of  thyroid  cartilage. 

Action. — As  preceding. 

Nerve. — First  cervical. 

Fig.  6. 


LATERAL   VIEW   OF  THE   NECK;    MIDDLE    LAYER   OF   MUSCLES. 

Funicular  portion  of  the  cervical  ligament;  2,  Complexus  major;  3,  Complexus 
minor;  4,  Rectus  capitis  posticus  major;  5,  Rectus  capitis  posticus  minor;  6, 
Stylo-maxillaris;  7,  Carotid  artery;  8,  Pneumogastric  nerve  and  branch  of  sym- 
pathetic; 9,  Longus  colli;  10,  Recurrent  nerve;  11,  Inferior  scalenus;  12,  Spinalis, 
or  transversalis  colli;  13,  Incision  through  rhomboideus  and  trapezius;  14,  Trachea. 


OMO-HYOID. 

Origin. — Inner  surface  of  sub-scapularis. 

Insertion. — Body  of  hyoid  bone  with  sterno-hyoid  (separates 
carotid  artery  fromJ'jugularVvein  in  upper  half  of  neck). 
Action. — Depresses^hyoid. 
Nerve. — First  cervical. 


MYOLOGY.  6 1 

RECTUS   CAPITIS   ANTICUS   MAJOR. 

Origin. — Transverse  process  of  third,  fourth  and  fifth  cervical 
vertebrae. 

Insertion. — Body  and  basilar  process  of  sphenoid. 
Action. — Flexes  head  or  carries  it  to  one  side. 
Nerve. — First  cervical. 

RECTUS   CAPITIS   ANTICUS   MINOR. 

Origin. — Inferior  surface  of  atlas. 

Insertion,  action,  nerve. — Same  as  preceding. 

RECTUS   CAPITIS   LATERALIS. 

Origin. — From  atlas  outside  preceding. 
Insertion. — Styloid  process  of  occipital. 
Action. — Depresses  head  laterally.  * 

Nerve. — First  cervical. 

SCALENUS   SUPERIOR. 

Origin. — Transverse  processes  of  last  three  or  four  cervical 
vertebrae. 

Insertion. — Superior  extremity  of  first  rib. 

Action. — Flexes  neck,   inclines  it  to  one  side,  or  raises  rib. 

Nerve. — Third  and  fourth  cervical. 

SCALENUS   INFERIOR. 

Origin. — Transverse   process  of  last  four  cervical   vertebrae. 
Insertion. — Anterior  border  and  external  face  of  first  rib. 
Action. — As  preceding. 
Nerve. — Third  and  fourth  cervical. 

LONGUS   COLLI. 

Origin;  Posterior  Portion. — Inferior  face  of  bodies  of  first  six 
dorsal  vertebrae. 

Insertion. — Inferior  tubercle  of  sixth  cervical  vertebrae. 

Origin;  Middle  Portion. — Transverse  process  of  last  six  cer- 
vical vertebrae. 

Insertion. — Inferior  ridge  of  bodies  of  first  six  cervical  vertebrae. 

Origin;  Anterior  Portion. — Anterior  three  or  four  fasciculi  of 
middle  portion. 


62  EQUINE   ANATOMY. 

Insertion. — Inferior  tubercle  of  atlas. 
Action. — Whole  muscle  flexes  neck. 
Nerve. — Third  and  fourth  cervical. 


REGION  OF  BACK. 

TRAPEZIUS. 

Origin. — Cervical  cord  and  transverse  processes  of  first  dorsal 
vertebrae. 
Insertion. — Olecranian  spine  and  scapular  aponeurosis. 
Action. — Raises  shoulder  and  carries  it  forward  or  backward. 
Nerve. — Spinal  accessory. 

LATISSIMUS   DORSI. 

Origin. — Spinous  processes  of  all  lumbar  and  last  fourteen  or 
fifteen  dorsal  vertebrae. 

Insertion. — Internal  tuberosity  of  body  of  humerus. 

Action. — Carries  arm  backward  and  upward,  also  in  forced  in- 
spiration. 

Nerve. — Eighth  cervical. 

SERRATUS   ANTICUS   MINOR. 

Origin. — Dorsal  spinous  processes  from  second  to  thirteenth. 
Insertion. — External  surface  of  ribs  from  fifth  to  fourteenth. 
Action. — Raises  ribs  in  inspiration. 
Nerve. — Intercostals. 

SERRATUS   POSTICUS   MINOR. 

Origin. — Spinous  processes  of  dorsal  vertebrae  from  tenth  to 
eighteenth,  and  few  lumbar  vertebrae. 

Insertion. — External  face  of  last  nine  ribs. 

Action. — Draws   ribs   upward   and   backward   in   expiration. 

Nerve. — Intercostals. 

ILIO- SPINALIS    (LONGISSIMUS   DORSI   OF   PERCIVAL). 

Origin. — Lumbar  border,  external  angle  and  internal  surface 
of  ilium,  and  spinous  processes  of  all  lumbar,  dorsal  and  last  four 
cervical  vertebrae. 


MYOLOGY.  63 

Insertion. — Transverse  processes  of  lumbar  vertebrae  and  outer 
surfaces  of  fifteen  or  sixteen  last  ribs. 

Action. — Extends  vertebral  column  and  pulls  ribs  forward  in 
expiration. 

Nerve. — Superior  dorsal. 

COMMON  INTERCOSTAL. 

Origin. — Runs  from  external  surface  of  one  rib  to  the  next ; 
the  anterior  fasciculus;  into  the  last  cervical  vertebra. 
Action. — Depresses  ribs. 
Nerve. — Intercostal. 

TRANSVERSE   SPINOUS   OF   BACK   AND   LOINS. 

Origin. — Lateral  lip  of  sacrum,  articular  tubercles  of  lumbar 
and  transverse  processes  of  dorsal  vertebrae. 

Insertion. — Spinous  process  of  sacral,  lumbar,  dorsal  and  last 
cervical  vertebrae. 

Action. — Extensor  of  spine. 

Nerve. — Superior  dorsal. 

COSTAL  REGION. 

Here  are  found  54  muscles: — ■ 

(1)  17  external  intercostals;  (2)  17  internal  intercostals;  (3) 
17  supercostals;  (4)  serratus  magnus;  (5)  costo-transversalis, 
and  (6)  triangularis  sterni. 

EXTERNAL  INTERCOSTALS. 

Origin. — Downward  and  backward  from  posterior  border  of 
rib  in  front. 

Insertion. — Anterior  border  of  rib  behind. 
Action. — Muscles  of  inspiration. 
Nerve. — I  ntercostal . 

INTERNAL  INTERCOSTALS. 

Origin. — Downward   and   forward,    crossing   preceding   from 
inner  and  anterior  border  of  rib  behind. 
Insertion. — Posterior  border  of  rib  in  front. 
Action. — Muscles  of  expiration. 
Nerve. — Intercostals. 


64  EQUINE   ANATOMY. 


SUPERCOSTALS. 


Origin. — From  transverse  processes  of  dorsal  vertebrae. 
Insertion. — External  surface  of  one  or  two  ribs  below. 
Action. — Draws  ribs  forward  in  inspiration. 
Nerve. — Superior  dorsal. 


SERRATUS   MAGNUS. 


Origin. — External  surface  of  first  eight  ribs. 
Insertion. — Anterior  and  posterior  triangular  surfaces  of  scapula 
and  subscapularis. 

Action. — Acts  to  support  body  as  a  girdle  or  depresses  scapula. 
Nerve. — Superior  thoracic. 


TRANSVERSE   COSTAL. 


Origin. — External  face  of  first  rib. 
Insertion. — Fourth  costal  cartilage  and  sternum. 
Action. — Raises  ribs  and  enlarges  thorax. 
Nerve. — Intercostal. 


TRIANGULARIS   STERNI. 

Origin. — From  superior  border  of  sternum. 
Insertion. — Cartilages  of  true  ribs  except  first. 
Action. — Expiratory  muscle  by  depressing  cartilages. 
Nerve. — Intercostal. 

DIAPHRAGM. 

The  muscular  partition  between  the  thoracic  and  abdominal 
cavities. 

Origin. — By  right  and  left  pillars  from  lumbar  vertebrae,  con- 
founded with  inferior  common  ligament  of  the  spine.  (Between 
two  pillars  pass  posterior  aorta  and  thoracic  duct.)  From  xiphoid 
appendix  of  sternum  and  anterior  extremities  of  last  twelve  ribs. 

Insertion. — Phrenic  centre,  dividing  into  right  and  left  leaflets. 

Relations. — Anteriorly,  with  pleurae  and  lungs;  posteriorly, 
peritoneum,  stomach,  liver,  colon  and  spleen. 

Openings. — Behind  for  aorta  and  thoracic  duct;  in  right  leaflet 
for  vena  cava;  in  right  pillar  for  oesophagus. 

Nerves. — Phrenic. 

Action. — Muscle  of  respiration. 


MYOLOGY.  65 

ABDOMINAL  REGION. 

EXTERNAL  OBLIQUE. 

Origin. — External  surface  of  thirteen  or  fourteen  lower  ribs 
and  aponeurosis  of  latissimus  dorsi. 

Insertion. — Into  linea  alba  and  pre-pubic  tendon.  A  number 
of  strong  fibres  are  reflected  from  the  pubes  to  the  anterior  su- 
perior spine  of  the  ilium,  forming  Poupart's  ligament. 

Action. — Compresses  abdominal  viscera,  flexes  spine  and  acts 
as  muscle  of  forced  expiration. 

Nerve. — Intercostal  and  lumbar. 

INTERNAL  OBLIQUE. 

•  Origin. — Aponeurosis  of  latissimus  dorsi;  external  angle  of 
ilium;  outer  fourth  of  Poupart's  ligament,  and  external  face  of 
last  few  ribs. 

Insertion. — Linea  alba;  the  fibres  separating  inferiorly  to  form 
part  of  the  inguinal  canal. 

Action. — Same  as  preceding. 

Nerve. — Intercostal  and  lumbar. 

RETRACTOR  OF   LAST   RIB. 

Origin. — From  transverse  processes  of  first  two  or  three  lum- 
bar vertebrae. 
Insertion. — Posterior  border  of  last  rib. 
Action. — Fixes  last  rib. 
Nerve. — Lumbar. 

TRANS  VERS  ALIS. 

Origin. — Internal  surface  of  asternal  ribs,  and  transverse  proc- 
esses of  lumbar  vertebrae. 

Insertion. — Into  linea  alba  (or  middle  aponeurosis  of  abdom- 
inal tunic)  and  crural  arch. 

Action. — Same  as  oblique  muscles. 

Nerve. — Intercostal  and  lumbar. 

RECTUS   ABDOMINIS. 

Origin. — To  cartilages  of  fifth,  sixth,  seventh,  eighth,  and  ninth 
ribs,  and  inferior  face  of  sternum. 

Insertion. — To  common  tendon  into  pubes. 


66  EQUINE   ANATOMY. 

Action. — Draws  pelvis  forward,  thorax  backward;  flexes  spine 
and  compresses  abdomen. 
Nerve. — Intercostal. 

INGUINAL  CANAL. 

A  canal  on  each  side  and  in  front  of  the  pubic  bone,  running 
downward,  backward  and  inward,  which  transmits  the  spermatic 
cord  and  vessels  in  the  male,  and  the  external  mammary  vessels 
in  the  female. 

Has  an  external  or  scrotal,  and  internal  or  peritoneal  ring,  and 
two  pillars. 

ANTERIOR  EXTREMITY. 

SUPERFICIAL  PECTORAL. 

Composed  of  two  parts. 

(A)  Sterno-humeralis. 

Origin. — Anterior  appendage  and  inferior  border  of  sternum. 
Insertion. — Anterior  ridge  of  humerus. 
Action. — Abductor  of  anterior  limb. 
Nerve. — Inferior  thoracic. 

(B)  Sterno-aponeuroticus. 

Origin. — Inferior  surface  of  sternum. 
Insertion. — With  preceding,'  and  also  into  fascia  of  limb. 
Action. — Same  as  preceding,  and  tensor  of  brachial  fascia. 
Nerve. — Inferior  thoracic. 

DEEP   PECTORAL. 

Composed  of  two  parts. 

(A)  Sterno-trochineus. 

Origin. — Abdominal  tunic  and  posterior  two-thirds  of  inferior 
border  of  sternum. 

Insertion. — Internal  tubercle  of  head  of  humerus,  fascia  of 
coraco-brachialis  and  coraco-radialis,  and  lip  of  bicipital  groove. 

Action. — Pulls  limb  backward. 

Nerve. — Inferior  thoracic. 


MYOLOGY.  67 

(B)  Sterno-prescapularis. 

Origin. — Sides  of  inferior  border  of  sternum,  and  cartilages  of 
first  three  or  four  ribs. 

Insertion. — Supra-spinatus  fascia. 

Action. — Pulls  scapula  backward  and  downward. 

Nerve. — Sixth  and  seventh  cervical. 

ANTEA   SPINATUS. 

Origin. — Antea-spinous  fossa. 

Insertion. — By  two  tendons  into  external  and  internal  humeral 
tubercles. 

Action. — Extensor  of  humerus. 
Nerve. — Sixth  and  seventh  cervical. 

POSTEA   SPINATUS. 

Origin. — Postea-spinous  fossa,  acromion  spine  and  tuberosity. 
Insertion. — External  humeral  tuberosity. 
Action. — Abductor  and  external  rotator. 
Nerve. — Sixth  and  seventh  cervical. 

TERES  MAJOR. 

Origin. — One  head  from  dorsal  angle  and  the  other  from 
aponeurosis  and  tuberosity  of  spine  of  scapula. 
Insertion. — Deltoid  imprint  of  humerus. 
Action. — Abductor  and  external  rotator. 
Nerve. — Eighth  cervical. 

TERES   MINOR. 

Origin. — Posterior  border  and  postea-spinous  fossa  of  scapula 
and  margin  of  glenoid  cavity. 

Insertion. — Humerus  between  external  and  deltoid  tuberosities. 
Action. — Like  preceding. 
Nerve. — Circumflex. 

SUBSCAPULARIS. 

Origin. — Subscapular  fossa. 
Insertion. — Internal  tubercle  of  humerus. 
Action. — Adductor  and  internal  rotator. 
Nerve. — Seventh  cervical. 


68  EQUINE  ANATOMY. 

ADDUCTOR   OF   THE   ARM. 

Origin. — Dorsal  angle  of  humerus  and  subscapularis. 
Insertion. — Circular  imprint  of  humerus. 
Action. — As  name  implies,  also  internal  rotator. 
Nerve. — Eighth  cervical. 

CORACO-BRACHIALIS. 

Origin. — Coracoid  process. 

Insertion. — Above  internal  tuberosity  and  anterior  face  of 
humerus. 

Action. — Adductor  internal  rotator. 
Nerve. — Musculo-cutaneous. 

SMALL   SCAPULO-HUMERALIS. 

Origin. — Above  glenoid  cavity. 

Insertion. — Into  capsular  ligament. 

Action. — Raises  capsular  ligament  during  flexion. 

Nerve. — Subscapular. 

BRACHIAL  REGION. 

CORACO-R  ADIALIS . 

Origin. — Coracoid  process  through  bicipital  groove. 
Insertion. — Bicipital  tuberosity  on   superior  and  inner  border 
of  radius,  capsular  and  internal  lateral  ligament. 
Action. — Flexes  forearm. 
Nerve. — Musculo-cutaneous. 

HUMERO-RADIALIS. 

Origin. — Posterior  face  of  humerus  below  head. 

Insertion. — Passes  through  groove  on  radius  under  internal 
lateral  ligament  into  upper  end  of  radius  and  ulna.  (Winds 
through  twisted  furrow  of  humerus.) 

Action. — Flexes  forearm. 

Nerve. — Radial. 

LONG  EXTENSOR  OF  FOREARM. 

Origin. — Aponeurosis  from  posterior  border  of  scapula. 
Insertion. — Posterior  border  of  ulna  and  anti-brachial  aponeuro- 
sis. 


MYOLOGY.  69 


Action. — Extends  forearm. 
Nerve. — Radial. 


LARGE  EXTENSOR  OF  FOREARM. 

Origin. — Dorsal  angle  and  axillary  border  of  scapula. 
Insertion. — Into  olecranon,  after  gliding  over  a  bursa. 
Action. — As  preceding. 
Nerve. — Radial. 

SHORT  EXTENSOR  OF  FOREARM. 

Origin. — Line  running  from  head  of  humerus  to  deltoid. 
Insertion. — Imprint  with  preceding. 
Action. — With  preceding. 
Nerve. — Radial. 

MIDDLE  EXTENSOR  OF  FOREARM. 

Origin. — Inner  surface  of  humerus  above  tuberosity. 
Insertion. — Tip  and  side  of  olecranon. 
Action. — As  preceding. 
Nerve. — Radial. 

ANCONEUS. 

Origin. — Above  margin  of  olecranian  fossa. 
Insertion. — Anterior  and  external  border  of  olecranon. 
Action. — Raises  capsule   of   humero-ulnar-radial   articulation. 
,  Nerve. — Radial. 

FOREARM. 

The  anti-brachial  aponeurosis  is  a  strong  layer  of  fibrous  tissue 
that  binds  the  muscles  of  the  forearm  together  and  passes  between 
them,  forming  the  inter-muscular  septum.  It  is  attached  to 
the  olecranon  and  sides  of  radius. 

ANTERIOR  EXTENSOR  OF  THE  METACARPUS. 

Origin. — From  humerus  below  crest  of  furrow  of  torsion,  and 
above  and  in  front  of  the  inferior  articular  portion. 

Insertion. — Anterior  and  superior  tuberosity  of  large  meta- 
carpal bone. 

Action. — As  name  implies. 

Nerve. — Radial. 


7o 


EQUINE   ANATOMY. 


Fig.  7. 


OBLIQUE  EXTENSOR  OF  METACARPUS. 

Origin. — External  surface  of  ra- 
dius. % 

Insertion. — Head  of  internal  me- 
tacarpal with  internal  lateral  liga- 
ment. 

Action. — Extends  metacarpus  and 
rotates  them  outward. 

Nerve. — Radial. 

ANTERIOR  EXTENSOR  OF  PHALANGES. 

Origin. — Below  crest  of  furrow  of 
torsion,  of  humerus,  and  in  front 
of  its  inferior  extremity;  the  ex- 
ternal lateral  ligament  of  elbow  and 
external  tuberosity  and  border  of 
radius. 

Insertion. — Pyramidal  eminence 
of  third  phalanx,  capsular  ligament 
of  fetlock- joint  and  anterior  surfaces 
of  first  and  second  phalanges. 

Action. — As  name  implies. 

Nerve. — Radial. 


Fig.  7.— External  muscles  of  the  right 
anterior  limb. 

i,  i,  Long  abductor  of  the  arm;  1'.  Its  humeral 
insertion;  2,  Superspinatus;  3,  Subspinatus; 
3',  Its  tendon  of  insertion;  4.  Short  ab- 
ductor of  the  arm;  5,  Biceps;  6,  Anterior 
brachialis;  7,  Large  extensor  of  the  fore- 
arm; 8,  Short  extensor  of  the  forearm;  9, 
Anconeus;  II,  Anterior  extensor  of  the 
metacarpus;  ir,  Its  tendon;  i2,Aponeurosis 
separating  that  muscle  from  the  anterior 
brachialis;  13,  Oblique  extensor  of  the 
metacarpus;  14,  Anterior  extensor  of  the 
phalanges;  14',  Its  principal  tendon;  15, 
The  small  tendinous  branch  it  furnishes  to 
the  lateral  extensor;  16,  Lateral  extensor  of 
the  phalanges;  i6\  Its  tendon;  17,  The 
fibrous  band  it  receives  from  the  carpus; 
18,  External  flexor  of  the  metacarpus;  19, 
Its  metacarpal  tendon;  20,  Its  supracarpal 
tendon;  21,  Ulnar  portion  of  the  perforans; 
22,  Tendon  of  the  perforans;  23,  Its  carpal 
ligament;  24,  Its  reinforcing  phalangeal 
sheath;  25,  Tendon  of  the  perforatus. 


MYOLOGY.  71 

LATERAL  EXTENSOR  OF  PHALANGES. 

Origin. — Outer   side  of  superior  tuberosity  of   radius;   from 
continuous  sides  of  radius  and  ulna  and  external  lateral  ligament. 
Insertion. — Anterior  surface  of  superior  portion  of  first  phalanx. 
Action. — As  preceding. 
Nerve. — Radial. 

EXTERNAL  FLEXOR  OF   METACARPUS. 

Origin. — External   condyle   of   humerus. 

Insertion. — Supercarpal  and  external  metacarpal  bones. 

Action. — Flexes  foot. 

Nerve. — Radial. 

OBLIQUE  FLEXOR   OF   METACARPUS. 

Origin. — Base  of  epitrochlea  and  olecranon. 
Insertion. — On  supercarpal  with  preceding. 
Action. — As  preceding. 
Nerve. — Ulnar. 

INTERNAL  FLEXOR  OF  METACARPUS. 

Origin. — Epitrochlea  with  preceding. 
Insertion. — Head   of    internal    metacarpal    bone. 
Action. — Same   as   external   flexor. 
Nerve. — Radial. 

FLEXOR   SUBLIMIS   DIGITORUM   OR  PERFORATUS. 

Origin. — Summit  of  epitrochlea. 

Insertion. — By  two  divisions  into  superior  extremity  of  second 
phalanx;  between  the  two  divisions  passes  the  perforans  tendon. 
It  also  passes  through  the  carpal  sheath,  a  reflexion  of  strong 
fibres  running  from  the  first  to  the  fourth  carpal  bones. 

Action. — Flexes  second  phalanx  and  also  whole  foot. 

Nerve. — Ulnar. 

FLEXOR  PROFUNDUS   DIGITORUM   OR  PERFORANS. 

Origin. — Summit  of  epitrochlea,  summit  and  posterior  border 
of  olecranon  and  posterior  surface  of  radius. 

Insertion. — Passes  through  carpal  sheath,  between  two  heads 


72  EQUINE   ANATOMY. 

of  perforatus,  and  is  attached  by  means  of  plantar  aponeurosis 
into  semi-lunar  crest  of  os  pedis. 

Action. — Flexes  third  phalanx  and  also  whole  foot. 

Nerve. — Ulnar.  t 

ANTERIOR  FOOT. 

They  comprise  two  lumbricales  and  two  interossei. 

LUMBRICALI. 

Origin. — From  right  and  left  side  of  perforans  tendon. 
Insertion. — Into  fibrous  tissue  of  the  fetlock. 

INTEROSSEI. 

Origin. — Anteriorly  between  metacarpal  bones. 
Insertion. — Into  anterior  extensor  of  phalanges. 
Action. — With  extensor. 
Nerve. — Ulnar. 

POSTERIOR  EXTREMITY. 

Pelvic  Region. — great  psoas. 

Origin. — From  bodies  of  last  two  dorsal  and  first  five  lumbar 
vertebrae,  inferior  surface  of  last  two  ribs  and  lumbar  transverse 
processes. 

Insertion. — Internal  trochanter. 

Action. — Flexor  and  external  rotator  of  thigh. 

Nerve. — Iliaco-muscular. 

ILIO-PSOAS. 

Origin. — Whole  iliac  surface,  external  iliac  angle,  sacro-iliac 
ligament  and  ilio-pectineal  crest. 
Insertion. — With  preceding. 
Action. — Same. 
Nerve. — Iliaco-muscular. 

SMALL  PSOAS. 

Origin. — Bodies  of  three  or  four  last  dorsal  and  all  lumbar 
vertebrae. 

Insertion. — Ilio-pectineal  eminence  and  ilio-lumbar  aponeurosis. 
Action. — Flexes  pelvis  on  spine,  or  spine  on  pelvis. 
Nerve. — Iliaco-muscular. 


73 


MUSCLES    OF   THE    SUB-LUMBAR,    PATELLAR.   AND   INTERNAL   CRURAL   REGIONS. 

Psoas  magnus;  i\  Its  terminal  tendon;  2,  Psoas  parvus;  3.  Uiacus;  4.  Its  small 
internal  portion;  5,  Muscle  of  the  fascia  lata;  6,  Rectus  of  the  thigh;  7,  Vastus 
internus;  8,  Long  adductor  of  the  leg;  9,  Short  adductor  of  the  leg;  11,  Pectineus; 
12,  Great  adductor  of  the  thigh;  12',  Small  adductor  of  the  thigh;  13,  Semimem- 
branosus; 14,  Semitendinosus.— a,  Portion  of  the  iliac  fascia;  b,  Portion  of  the 
layer  reflected  from  the  aponeurosis  of  the  abdominal  great  oblique,  forming 
Poupart's  ligament;  c,  Pubic  tendon  of  the  abdominal  muscles;  d,  Origin  of  the 
pubo-femoral  ligament. 
6 


74  EQUINE   ANATOMY. 

QUADRATUS   LUMBORUM. 

(A)  Primary  Fasciculus. 

Origin. — Sacroiliac  ligament. 

Insertion. — Last  rib  and  transverse  lumbar  processes. 

(B)  Secondary  Fasciculus. 
Origin. — From  first. 

Insertion. — Lumbar  transverse  processes  and  last  two  or  three 
ribs. 

Action. — Draws  last  rib  backward  and  inclines  spine  laterally. 
Nerve. — Lumbar. 

INTER-TRANSVERSE   OF   LOINS. 

Runs  between  lumbar  transverse  processes. 
Action. — Inclines  lumbar  region  laterally. 
Nervt. — Lumbar. 

Gluteal  Region. — superficial  gluteal. 

Origin. — Internal    aspect    of    gluteal    aponeurosis,    postero- 
external iliac  angle  and  ischiatic  ligament. 
Insertion. — Third  trochanter  of  femur. 
Action. — Abductor  and  external  rotator  of  femur. 
Nerve. — Anterior  gluteal. 

MIDDLE  GLUTEAL. 

(Largest  of  three.) 

Origin. — Gluteal  aponeurosis,  superior  face  and  external  angles 
of  ilium,  sacro-iliac  and  sacro-sciatic  ligaments. 
Insertion. — Trochanter  major. 
Action. — Abductor  of  thigh,  or  assists  in  rearing. 
Nerve. — Anterior  gluteal. 

DEEP  GLUTEAL. 

Origin. — Neck  of  ilium  and  supra-cotyloid  ridge. 
Insertion. — Convexity  of  trochanter. 
Action. — Abductor  and  internal  rotator. 
Nerve. — Posterior  gluteal. 


MYOLOGY. 


75 


Thigh. — tensor  vaginae  femoris. 
Origin. — External  angle   of  ilium. 

Insertion. — Into  the  strong  fascia  covering  and  running  be- 
tween the  muscles  of  the  thigh,  the  fascia  lata. 

Action. — Flexes  thigh  and  renders  fascia  lata  tense. 
Nerve. — Anterior  gluteal. 

CRURAL  TRICEPS. 

(A)  Rectus. 

Origin. — Lip  of  cotyloid  cavity. 
Insertion. — Into  patella. 

(B)  Vastus  Externus. 

Origin. — Outer  and  anterior  surfaces  of  femur. 
Insertion. — As  above. 

(C)  Vastus  Internus. 

Origin. — Inner  and  anterior  surfaces  of  femur. 
Insertion. — As  above. 
Action. — Extensor  of  leg.. 
Nerve. — Posterior  gluteal. 

ANTERIOR  GRACILIS. 

Origin. — From  ilium  near  origin  of  rectus. 
Insertion. — Into  capsular  ligament  of  hip  joint. 
Action. — Makes  tense  capsule  of  joint. 
Nerve. — Ilio-muscular. 

LONG  VASTUS. 

(A)  Anterior  portion. 

Origin. — Sacral  spine,  sacro-sciatic  ligament,  tuberosity  of 
ischium  and  coccygeal  aponeurosis. 

Insertion. — Below  subtrochanteric  crest  of  femur  and  side  of 
patella. 

Action. — Pulls  femur  backward  and  patella  outward. 

(B)  Posterior  portion. 

Origin. — Spine  and  tuberosity  of  ischium. 
Insertion. — Crest  of  tibia  and  tibial  fascia. 
Action. — Flexes  leg  and  makes  tense  fascia. 
Nerve. — Great  sciatic. 


76  •  EQUINE  ANATOMY. 

SEMI-TENDINOSUS . 

Origin. — From  sacral  spine,  sacro-sciatic  ligament  (with  long 
vastus  and  tuber  ischii). 
Insertion. — Anterior  crest  of  tibia. 
Action. — Same  as  preceding. 
Nerve. — Great  sciatic. 

SEMI-MEMBRANOSUS. 

Origin. — Tuberosity  and  inferior  face  of  body  of  ischium  and 
coccygeal  aponeurosis. 

Insertion. — Eminence  above  internal  condyle  of  femur. 

Action. — Adductor  and  extensor  of  thigh  and  an  adjunct  in 
rearing. 

Nerve. — Great  sciatic. 

Internal  Femoral  Region. — sartorius. 

Origin. — Iliac  aponeurosis  near  tendon  of  psoas  parvus. 
Insertion. — Internal  patellar  ligament. 
Action. — Adducts  leg  and  flexes  femur. 
Nerve. — Obturator. 

GRACILIS. 

Origin. — Ischio-pubic  symphysis. 

Insertion. — With  preceding  and  internal  tuberosity  of  tibia. 
Action. — Adductor  of  leg  and  tensor  of  tibial  aponeurosis. 
Nerve. — Obturator. 

PECTINEUS. 

Origin. — Inferior  face  of  pubes  of  pubo-femoral  ligament. 
Insertion. — Inner  surface  of  femur  near  nutrient  foramen. 
Action. — Adductor,  flexor  and  internal  rotator  of  femur. 
Nerve. — Obturator. 

ADDUCTOR  BREVIS. 

Origin. — Inferior  face  of  pubis. 

Insertion. — Quadrilateral  line  on  posterior  surface  of  femur. 

Action. — As  name  implies. 

Nerve. — Obturator.  * 

ADDUCTOR   LONGUS. 

Origin. — Lower  face  of  ischium  and  symphysis. 

Insertion. — With  preceding,  and  internal  condyle  of  femur. 


MYOLOGY.  77 

Action. — Adductor,  extensor  and  external  rotator  of  thigh. 
Nerve. — Obturator. 

QUADRATUS   FEMORIS. 

Origin. — Tuber  ischii. 

Insertion. — Posterior  surface  of  femur,  below  trochanter. 

Action. — Extensor  and  adductor  of  femur. 

Nerve. — Great  sciatic. 

EXTERNAL   OBTURATOR. 

Origin. — Below  margin  of  obturator  foramen. 
Insertion. — Trochanterian  fossa. 
Action. — Adductor  and  external  rotator. 
Nerve. — Obturator. 

INTERNAL   OBTURATOR. 

Origin. — Above  margin  of  obturator  foramen. 
Insertion. — Trochanterian  fossa. 
Action. — Abductor  and  external  rotator. 
Nerve. — Great  sciatic. 

GEMELLI. 

Origin. — Above  and  below  tendon  of  obturator  internus,  from 
ischium. 

Insertion. — Into  tendon  of  internal  obturator. 
Action. — Like  preceding. 
Nerve. — Great  sciatic. 

ANTERIOR  EXTENSOR  OF  PHALANGES. 

Origin. — Digital  fossa  above  external  condyle  of  femur. 

Insertion. — Capsular  ligament  of  metatarso-phalangeal  articu- 
lation, anterior  surfaces  of  first  two  phalanges,  and  pyramidal 
eminence  of  os  pedis. 

Action. — Extends  digit. 

Nerve. — External    popliteal.    - 

LATERAL  EXTENSOR  OF  PHALANGES. 

Origin. — External  femoro-tibial  ligament  and  whole  extent  of 
fibula. 

Insertion. — Terminates  in  tendon  of  anterior  extensor. 
Action. — As  preceding. 
Nerve. — External  popliteal. 


78 


EQUINE   ANATOMY. 
Fig.  g. 


MUSCLES    ON    INNER   ASPECT   OF   LEFT   POSTERIOR    LIMB. 

Crest  of  the  ilium;  2,  Section  through  it;  3,  Sacro-ischiatic  ligament;  4,  Pyriformis; 
5,  Posterior  portion  of  sacro-ischiatic  ligament;  6,  Tuberosity  of  ischium;  7,  An- 
terior portion  of  ischium,  sawn  through;  8,  Pubis;  9,  Obturator  foramen;  10,  Ex- 
ternal iliac  artery  and  vein,  11;  12,  Obturator  artery  and  vein;  the  figures  are 
placed  on  the  internal  obturator  muscle;  13,  Long  adductor  of  the  leg,  or  sar- 
torius;  14,  Small  adductor  of  the  thigh,  or  adductor  brevis;  15,  Short  adductor  of 
the  leg,  or  gracilis;  t6,  Rectus  of  the  thigh;  17,  Vastus  internus;  18,  Patella,  with 
insertion  of  rectus;  19,  Upper  extremity  of  tibia;  20,  Gastrocnemius;  21,  Pop- 
liteus;  22,  Oblique  flexor  of  the  phalanges,  or  flexor  pedis  accessorius,  with  its 


MYOLOGY.  .  79 

tendon,34;  23,  Perforans  muscle,  with  its  tendon,  35;  24.  Flexor  metatarsi;  25,  An- 
terior extensor  of  the  phalanges,  or  extensor  pedis;  26,  Annular  ligament;  27,  Ten- 
don of  flexor  metatarsi,  and  its  cunean  branch,  28;  29,  Tendon  of  superficial  flexor, 
or  internal  gastrocnemius;  30,  Tendon  of  gemelli  or  external  gastrocnemius; 
si,  Os  calcis;  32,  Astragalus;  33,  Perforatus  tendon;  34,  Tendon  of  oblique  flexor 
joining  the  perforans  tendon,  35;  36,  Large  metatarsal  bone;  37,  Extensor  pedis 
tendon;  38,  Terminal  knob  of  small  metatarsal  bone. 


FLEXOR   OF   METATARSUS. 

(A)  Tendinous  Portion. 

Origin. — From  front  of  femur  between  trochlea  and  external 
condyle. 

Insertion. — Front  of  superior  extremity  of  principal  metatarsal 
and  cuboid. 

Action. — Flexes  metatarsus  and  hock  joint. 

(B)  Muscular  Portion. 

Origin. — From  tibia  on  sides  of  groove  for  tendinous  portion. 
Insertion. — In  front  of  superior  extremity  of  principal  meta- 
tarsal and  second  cuneiform  bone. 
Nerve. — Anterior  tibial. 

GASTROCNEMII. 

Origin. — External  head  from  above  and  behind  external  con- 
dyle.    Internal  from  internal  condyle. 

Insertion. — Into  posterior  part  of  summit  of  os  calcis  after  pass- 
ing over  a  bursa. 

Action. — Extends  foot  on  tibia. 

Nerve. — Great  sciatic. 

SOLEUS. 

Origin. — External  tuberosity  of  tibia. 
Insertion. — Into  tendon  of  preceding. 
Action. — As  preceding. 
Nerve. — Great  sciatic. 

FLEXOR   SUBLIMIS   DIGITORUM   OR   PERFORATUS. 

Origin. — Above  super-condyloid  fossa  of  femur. 
Insertion.— Into  summit  of  os  calcis  and  fibrous  band  of  hock, 
then   spreads   out   on   second   phalanx. 

Action. — Flexes  second  phalanx  and  extends  foot. 
Nerve. — Plantar. 


80  .  EQUINE    ANATOMY. 

POPLITEUS. 

Origin. — Outside  external  condyle  of  femur. 
Insertion. — Into  triangular  surface  on  posterior  surface  of  tibia 
at  its  upper  portion. 

Action. — Flexes  tibia  and  rotates  it  outward. 
Nerve. — Great  sciatic. 

FLEXOR  PROFUNDUS   DIGITORUM   OR  PERFORANS. 

Origin. — To  external  tuberosity  and  posterior  surface  of  tibia 
fibula  and  interosseous  ligament. 

Insertion. — Passes  through  tarsal  sheath  on  inner  side  of  os 
calcis  and  into  semilunar  crest  of  os  pedis. 

Action. — Flexes  phalanges  on  each  other  and  on  metatarsus. 

Nerve. — Great  sciatic. 

OBLIQUE  FLEXOR   OF   PHALANGES. 

Origin. — External  tuberosity  of  tibia. 
Insertion. — Upper  third  of  metatarsus. 
Action. — With  preceding. 
Nerve. — Great  sciatic. 

POSTERIOR  FOOT. 

Two  lumbricales  and  two  inter ossei,  as  in  anterior  foot. 

PEDAL  MUSCLE. 

Origin. — Lower  end  of  os  calcis  and  astragalus. 
Insertion. — Into  tendons  of  extensors  of  phalanges. 
Action. — Aids  in  extending  digit  and  flexing  hock. 
Nerve. — Plantar. 

Coccygeal  Region. — (3  pairs.)  sacro-coccygeus  superior. 
Origin. — From  side  of  spinous  processes  of  last  3  or  4  sacral 
vertebrae. 

Insertion. — Into  coccygeal  vertebrae. 

Action. — Elevates  tail  or  carries  it  to  one  side. 

Nerve. — Coccygeal. 

sacro-coccygeus  inferior. 

Origin. — From  third  portion  of  sacrum,  internal  surface  of 
sacro- sciatic  ligament. 


CIRCULATORY  APPARATUS.  8l 

Insertion. — Under  surface  of  coccygeal  vertebrae. 
Action. — Depresses  tail  or  carries  it  to  one  side. 
Nerve. — Coccygeal. 

SACRO-COCCYGEUS   LATERALIS. 

Origin. — Spinous  processes  of  last  lumbar  vertebrae. 
Insertion. — Sides   of   coccygeal   vertebrae. 
Action. — Carries  tail  to  one  side. 
Nerve. — Coccygeal. 

ISCHIO-COCC  YGEUS . 

Origin. — Internal  face  of  sacro-sciatic  ligament  and  sciatic 
crest. 

Insertion. — Last  sacral  and  first  two  coccygeal  vertebrae. 
Action. — Depresses  whole  tail. 
Nerve. — Coccygeal. 

CIRCULATORY   APPARATUS. 
PERICARDIUM. 

A  fibro-serous  membrane  enveloping  the  heart  and  favoring  its 
movement  by  its  polished  surfaces.  Fibrous  layer  attached  by  its 
apex  to  the  sternum^  from  the  fourth  rib  to  the  xiphoid  appendix. 

By  its  base  to  the  great  vessels  of  the  neck  and  continuous  with 
the  fascia  of  the  neck. 

Serous  layer  composed  of  a  layer  of  flattened  epithelium  on  a 
basement  membrane.  It  is  composed  of  two  divisions,  a  visceral 
and  parietal.  The  parietal  layer  is  reflected  on  the  fibrous  sac, 
and  the  visceral  over  the  heart  itself.  Amount  of  fluid  in  sac, 
very  small. 

Blood  supply  from  mediastinal  arteries. 

Nerves  from  sympathetic. 

HEART. 

The  heart  is  the  propelling  organ  of  the  blood.  It  is  a  hollow 
muscle  placed  in  the  thorax  opposite  the  third,  fourth,  fifth  and 
sixth  ribs,  between  and  below  the  lungs.  It  is  conoidal  in  shape, 
10  inches  long  and  7J  inches  wide.     Weight,  6}  lbs. 


EQUINE  ANATOMY. 
Fig.  io. 


THE   HEART   AND    PRINCIPAL   VESSELS;    LEFT    FACE. 

Right  ventricle;  b.  Left  ventricle;  c,  Right  auricle;  d,  Left  auricle;  e,  Pulmonary 
artery;  e! ',  Obliterated  arterial  canal;  /,  Pulmonary  veins;  g,  Anterior  aorta;  h. 
Left  axillary  artery;  i,  Right  a*xillary  artery,  or  brachio-cephalic  trunk;  /,  Origin 
of  the  dorsal  artery;  k,  Origin  of  the  superior  cervical  artery;  /,  Origin  of  the 
vertebral  artery;  m,  Origin  of  the  inferior  cervical  artery;  «,  Origin  of  the  in- 
ternal thoracic  artery;  o.  Origin  of  the  external  ditto;  p,  Carotid  arteries;  g,  Pos- 
terior aorta;  r,  Anterior  vena  cava;  s,  Trunk  of  the  axillary  vein;  t,  Trunk  of  the 
internal  thoracic  vein;  u,  Trunk  of  the  dorso-cervical  vein;  v,  Posterior  vena 
cava;  v' ,  Embouchure  of  the  hepatic  and  diaphragmatic  veins;  x.  Vena  azygos; 
y,  Thoracic  duct;  z,  Embouchure  of  that  vessel,  placed  near  the  origin  of  the 
anterior  vena  cava,  i,  Right  cardiac  artery;  2,  Left  cardiac  artery;  3;  Auriculo- 
ventricular  branch  of  the  latter;  4,  Its  ventricular  branch;  5,  Cardiac  vein. 


CIRCULATORY  APPARATUS.  83 

Cavities. — It  is  divided  by  a  vertical  septum  into  two  parts, 
which  are  further  divided  into  four  by  a  transverse  septum. 

The  cavities  above  the  transverse  septum  are  called  the  right 
and  lejt  auricles. 

Those  below,  the  right  and  lejt  ventricles. 

RIGHT   AURICLE. 

On  an  average  the  walls  are  one-fourth  of  an  inch  thick.  It 
receives  the  anterior  vena  cava,  posterior  cava  vena  azygos,  and 
the  large  coronary  veins,  and  opens  into  the  interior  of  the  auric- 
ular appendix,  a  mass  projecting  from  the  outside  of  the  auricle. 
Its  interior  is  divided  by  a  number  of  transverse  bands  called*  mus- 
culi  pectinati. 

On  the  posterior  wall  is  the  fossa  ovalis,  the  remains  of  the  open- 
ing existing  in  fcetal  life;  around  its  periphery  is  found  the  annulus 
ovale  or  ring. 

Behind  the  anterior  cava  is  an  eminence,  the  tuberculum  Loweri. 
The  anterior  border  of  the  fossa  ovalis  shows  a  fold  called  the 
Eustachian  valve,  a  remnant  of  fcetal  life. 

The  auriculo-ventricular  opening  is  found  on  its  floor,  circular 
in  outline,  surrounded  by  a  fibrous  ring  and  closed  by  the  tricus- 
pid valve. 

RIGHT  VENTRICLE. 

The  walls  are,  on  an  average,  y6^  of  an  inch  thick.  The  apex 
extends  to  only  ij  inches  from  the  point  of  the  heart.  The  walls 
are  uneven  from  the  columnae  carnece,  or  muscular  columns, 
which  project  into  the  cavity.  They  are  of  three  varieties,  one 
attached  by  one  end  and  the  other  prolonged  by  the  chordae  ten- 
ding, to  the  edges  of  the  valves;  the  second,  by  both  extremities; 
the  third,  adherent  through  all  its  length. 

The  tricuspid  valve  closes  the  opening  into  the  auricle,  and  is 
composed  of  three  segments,  all  attached  to  the  chorda  tendince. 

The  pulmonary  opening  is  circular  and  leads  into  the  pulmonary 
artery.  It  is  closed  in  by  the  semilunar  valves,  three  in  number, 
which  are  attached  also  to  the  tendinous  cords.  In  the  centre  of 
each  valve  is  often  seen  an  elevation,  the  corpus  arantii. 

LEFT  AURICLE. 

Much  similar  in  structure  to  that  of  the  right  side.  It  opens 
into  the  left  ventricle,  and  has  on  its  superior  wall  the  openings 


84  EQUINE   ANATOMY. 

of  four  to  eight  pulmonary  veins,  which  have  no  valves.     The 
obliterated  foramen  ovale  is  also  seen  on  the  inter-auricular  septum. 

LEFT   VENTRICLE. 

The  walls  are  on  an  average  i^  to  if  inches  in  thickness;  at  the 
apex  they  are  very  thin  and  form  the  point  of  the  heart. 

The  auriculo-ventricular  opening,  similar  to  that  on  the  right 
side,  is  closed  by  the  mitral  valve,  composed  of  two  segments  at- 
tached to  chordae  tendinae. 

The  aortic  opening  is  similar  to  the  one  on  the  right,  and  is 
closed  by  the  semilunar  valves. 

Structure. 

Four  fibrous  rings  around  the  openings. 

At  the  junction  of  the  aortic  and  auriculo-ventricular  rings  is  a- 
cartilaginous  body. 

The  muscular  tissue  is  striped  and  involuntary,  but  unlike  all 
voluntary  tissue,  it  inosculates  and  branches  freely,  has  no  sarco- 
lemma,  and  its  striae  are  not  well  marked. 

The  auricles  have  two  sets  of  fibres,  one  common  to  both,  the 
other  of  fasciculi  arranged  in  loops,  rings,  or  as  sphincters. 

The  ventricles  have  also  two  sets,  one  intrinsic  running  from  the 
rings  obliquely  around  the  axis  of  the  ventricle,  the  other  common 
to  both,  running  downward  and  from  left  to  right,  terminating  in- 
ternally in  the  columnce  carnece. 

The  endocardium  is  a  serous  membrane  lining  the  cavities  of 
the  heart,  having  a  basement  membrane  covered  with  flattened 
endothelium,  polygonal  in  form,  each  with  a  nucleus.  Its  redu- 
plications form  the  valves. 

Blood  supply. 

Coronary  arteries,  from  trunk  of  the  aorta,  each  following  the 
horizontal  and  vertical  furrows.  The  venous  blood  is  returned  to 
the  right  auricle  by  the  coronary  vein. 

Nerves. 

From  pneumogastric  and  sympathetic.  Probably  also  intra- 
cardiac sympathetic  ganglia. 

ARTERIES. 

The  arteries  are  the  tubes  that  carry  arterial  blood  from  the 
heart  over  the  body. 

The  pulmonary  artery  carries  venous  blood  to  the  lungs,  form- 


CIRCULATORY  APPARATUS.  85 

ing  with  the  corresponding  veins  the  pulmonary  circulation.  The 
remainder  of  the  arteries  constitute  the  general  or  systemic  circu- 
lation. 

Structure  of  arteries. 

They  are  more  or  less  rigid  and  elastic,  with  three  coats — (i) 
an  external  fibrous  or  adventitia,  (2)  a  middle  muscular  or  mediaf 
(3)  an  internal  serous  or  intima,  continuous  with  the  endocar- 
dium. 

The  external  tunic  is  nourished  by  vasa  vasorum,  and  the  mus- 
cular coat  receives  branches  from  the  sympathetic  system,  called 
vasomotor  nerves. 

The  capillaries  are  small  vessels  between  the  arterial  and  venous 
systems.  They  are  composed  of  a  basement  membrane,  covered 
by  a  layer  of  delicate  cells,  continuous  with  those  of  the  arteries. 

THE  AORTA. 

It  is  the  beginning  of  the  arterial  system,  given  off  from  the 
left  ventricle,  and  guarded  by  the  semilunar  valves.  Just  above 
the  valves  it  shows  three  dilatations,  the  sinuses  of  Valsalva.  It 
passes  upward  and  forward  for  about  two  inches,  when  it  divides 
into  the  anterior  and  posterior  aortas. 

Branches. 

Right  and  left  coronary  to  heart  (see  above). 

ANTERIOR  AORTA. 

The  smaller  of  the  two  passes  forward  and  upward  for  two  or 
two  and  a  half  inches,  where  it  divides  into  the  two  axillary  arteries 
or  brachial  trunks. 

The  right  is  much  the  larger,  and  gives  off  the  carotid  arteries. 

Course. 

They  curve  forward  and  outward  over  the  anterior  border  of 
the  first  rib  below  the  scaleni,  accompanied  by  the  brachial  nerves 
to  the  space  between  the  sub-scapularis  and  the  adductor  of  the 
arm,  where  it  becomes  the  humeral  artery. 

Branches. — From  thoracic  portion. 
1.  Dorsal  or  transverse  cervical. 
To  muscles  and  integument  of  the  withers,  neck  and  shoulders. 


86  EQUINE   ANATOMY. 

It  gives  off  the  sub-costal,  which  sends  branches  to  the  second, 
third  and  fourth  intercostal  spaces. 

2.  Superior  or  deep  cervical. 

Passes  between  first  two  ribs  to  muscles  of  neck  or  back,  to 
spinal  cord  and  first  intercostal  space. 

3.  Vertebral. 

Through  foramina  of  the  upper  six  cervical  vertebrae,  anasto- 
mosing with  the  occipital,  and  giving  off  muscular  and  spinal 
branches,  called  superior,  inferior,  external  and  internal. 

4.  Internal  thoracic  or  internal  mammary. 

Given  off  near  the  first  rib;  runs  above  the  costal  cartilages  to 
the  xiphoid  appendix. 

Branches. 

Superior  to  pericardium  and  mediastinum;  inferior  to  pectoral 
muscles,  external  or  intercostal;  anterior  abdominal  passes  into 
rectus  muscle  and  anastomoses  with  post-abdominal. 

Asternal  artery  to  thirteenth  intercostal  space,  anastomosing 
with  artery;  gives  off  abdominal,  intercostal  and  diaphragmatic 
branches. 

5.  External  thoracic  or  external  mammary. 

Given  off  in  front  of  preceding,  curving  around  first  rib;  sup- 
plies pectoral  and  other  muscles  of  chest. 

6.  Inferior  cervical. 

Given  off  opposite  the  two  preceding;  divides  into  two  branches, 
superior  (ascending  cervical)'  to  muscles  and  glands  of  neck, 
and  inferior  (acromio-thoracic)  to  pectoral  muscles. 

7.  Superior  scapular. 

Given  off  near  sub-scapular  tendon;  passes  up  and  terminates 
in  scapular  muscles  and  shoulder  joint. 

8.  Sub-scapular. 

Given  off  at  junction  of  axillary  portion  with  humeral  artery; 
passes  up  and  backward  near  the  dorsal  angle  of  scapula. 

Branches. 

One  to  latissimus  dor  si. 

Muscular  branches  to  scapular  muscles. 

Scapulo-humeral  to  muscles  of  shoulder  and  arm. 

HUMERAL  ARTERY. 

From  posterior  border  of  sub-scapularis  muscle  to  above  in- 


CIRCULATORY  APPARATUS.  87 

ferior  articular  surface  of  the  humerus,  where  it  terminates  in  the 
anterior  and  posterior  radial  arteries. 

It  is  in  relation  to  the  median  nerve  on  the  outside  and  the 
coraco-radialis  on  the  inside. 

Its  branches  are — 

1.  Prehumeral  or  anterior  circumflex  of  shoulder. 

To  shoulder  joint  and  muscles  of  upper  humeral  region,  anasto- 
mosing with  posterior  circumflex. 

2.  External  collateral  of  elbow. 

To  muscles  in  vicinity  of  elbow  joint,  where  it  anastomoses 
with  anterior  radial. 

3.  Internal  collateral  or  ulnar. 

To  internal  border  of  arm  and  forearm,  to  carpus,  anastomo- 
sing with  posterior  radial,  and  accompanying  the  ulnar  nerve  and 
vein.     It  sends  branches  to  muscles,  to  elbow  joint  and  humerus. 

4.  Coraco-radial. 
To  muscle. 

ANTERIOR  RADIAL. 

The  smaller  of  two  branches  of  humeral  extends  along  front 
of  radius  to  front  of  carpus,  where  it  splits  up  into  smaller  branches, 
which  supply  the  articulation,  and  anastomose  with  posterior 
radial  and  interosseous.  It  gives  off  branches  also  to  elbow  joint 
and  muscles. 

POSTERIOR  RADIAL. 

The  larger  of  two  subdivisions  of  humeral,  passes  to  side  on 
internal  ligament  of  elbow,  along  inner  side  of  radius,  to  its  in- 
ferior portion,  where  it  divides  into  the  common  interosseous, 
metacarpal  and  collateral  artery  of  the  cannon. 

The  branches  in  its  course  are  to  elbow  and  muscles  of  forearm. 

INTEROSSEOUS   OF  FOREARM. 

Arises  near  radia-ulnar  arch,  and  passes  along  groove  between 
ulnar  and  radius.  Gives  off  branches  to  the  elbow,  anti-brachial 
muscles,  and  terminates  at  the  carpus  by  numerous  anastomoses. 


88 


EQUINE   ANATOMY. 


Fig.  ii. 


COMMON   INTEROSSEOUS   OF   METACARPUS. 

Given  off  at  inner  side  of,  and  descends  be- 
hind, the  carpus  to  the  head  of  internal  meta- 
carpal, then  passes  outward,  anastomosing  with 
a  descending  branch  from  arch  above  between 
ulnar  and  common  arteries,  forming  the  sub- 
carpal  arch.  That  above  is  the  supra-carpal 
arch. 

Branches. 

Two  posterior  interosseous,  arising  at  heads  of 
metacarpus,  pass  downward,  ending  at  the 
lower  ends  of  metacarpus,  anastomosing  with 
the  collateral  of  the  cannon,  and  giving  off 
branches  to  the  suspensory  ligament,  skin  and 
tendons. 

Two  anterior  interosseous,  arising  with  pre- 
ceding, curve  around  heads  of  bones,  become 
anterior,  pass  downward,  anastomose  with 
artery  of  cannon,  and  send  branches  to  tendons 
and  skin. 


^ 


COLLATERAL   ARTERY   OF   CANNON. 

Passes  under  carpal  sheath  to  inner  side  of 
flexor  tendons,  with  internal  plantar  nerve,  to 
top  of  great  sesamoid  bones,  where  it  divides 
into  the  digital  arteries. 

Fig.  ii,— Arteries  of  the  fore-foot,  seen  from  behind. 

The  muscles  and  tendons  have  been  removed,  only  a  small 
portion  of  the  perforans  tendon  being  left;  the  os  pedis 
has  been  chiseled  away  on  its  plantar  face  to  expose  the 
semilunar  anastomosis. 

i,  Posterior  radial  artery;  2,  Innominate  carpal  branch;  3, 
Supra-carpal  arch;  4,  Epicondyloid  (ulnar)  artery;  5, 
Radio-palmar  artery,  or  common  trunk  of  the  interosse- 
ous metacarpal  arteries;  6,  Sub-carpal  arch;  7,  7,  Poste- 
rior interosseous  meta-carpal  arteries;  7',  7f,  Anterior 
interosseous  metacarpal  arteries;  8,  8,  Their  origin;  9, 
Collateral  artery  of  the  cannon;  10,  Its  communicating 
branch  with  the  interosseous  arteries;  11,  11,  Digital  arte- 
ries; 12,  Semilunar  anastomosis  in  the  os  pedis;  13,  Emerg- 
ent branches  of  this  anastomosis;  14,  Plantar  ungueal 
artery,  forming  this  anastomotic  arch;  15,  Origin  of  the 
preplantar  ungueal  artery;  16,  Origin  of  the  plantar- 
cushion  artery;  17,  Origin  of  the  anterior  branch  of  the 
coronary  circle;  18,  Posterior  branch  of  the  same. 


CIRCULATORY  APPARATUS.  89 

Branches. 

An  anastomosing  branch,  with  the  internal  collateral  form- 
ing the  supra-carpal  arch  above  the  pisiform  bone. 

A  few  to  the  tendons  and  skin. 

One  passing  upwards,  anastomosing  with  the  interossei.  The 
digital  vessels  are  similar  to  those  of  the  posterior  limb,  with  which 
they  will  be  described. 

COMMON  CAROTIDS. 

These  two  vessels  supplying  the  head  and  neck,  arise  by  a  com- 
mon trunk,  from  the  right  axillary  at  its  origin,  called  the  cephalic. 
This  passes  forward  under  the  trachea  to  anterior  entrance  of  the 
chest,  where  it  divides  into  its  two  branches;  each  common  carotid 
passes  upward  along  the  trachea  to  the  larynx,  where  it  divides 
into  the  occipital,  external  and  internal  carotids. 
Branches. 

Small  ones  to  the  muscles,  oesophagus  and  trachea. 

Thyro-laryngeal,  to  thyroid  gland,  larynx  and  pharynx. 

Accessory  thyroid,  to  thyroid  and  cervical  muscles. 

Occipital. 

Passes  alongside  of  internal  carotid,  under  inferior  arch  of 
atlas,  through  anterior  foramen  in  its  transverse  process,  dividing 
into  occipito-muscular  and  cerebrospinal. 
Branches. 

Prevertebral,  to  muscles  of  neck  and  dura  mater. 

Mastoid,  through  parieto-temporal  canal  to  dura  and  temporal 
muscles. 

Atloido-muscular,  passes  backward  to  anastomose  with  vertebral. 

Occipito-muscular,  inward  to  muscles  and  skin  of  occipital 
region. 

Cerebrospinal. 

Enters  spinal  canal  and  divides  into  two  branches,  one  of  which 
passes  backward  and  unites  with  its  fellow  of  the  opposite  side, 
forming  the  median  spinal  artery.^  The  anterior  branch  unites 
with  its  fellow,  forming  the  basilar. 

Basilar. 

Passes  under  the  medulla,  runs  forward  to  the  anterior  border 
of  the  pons. 
Branches. 

Small  vessels  to  pons,  medulla  and  cranial  nerves. 

7 


9o 


EQUINE   ANATOMY. 
Fig.  12. 


ARTERIES    OF   THE    BRAIN. 

Medulla  oblongata;  p,  Pons  Varolii;  l,  Mastoid  lobule;  o,  Olfactory  lobule; 
c,  Chiasma  of  the  optic  nerves;  m,  Mammillary,  or  pisiform  tubercle;  h,  Pituitary 
gland;  three-fourths  have  been  excised,  i,  i,  Cerebrospinal  arteries;  2,  Median 
spinal  artery;  3,  Lozenge-shaped  anastomosis  of  the  two  cerebro-spinal  arteries, 
from  which  result,  in  front,  4,  The  basilar  trunk  (usually  the  cerebro-spinal  arter- 
ies arrive  in  the  middle  of  the  lozenge);  5,  5,  Posterior  cerebellar  arteries;  6,  An- 


CIRCULATORY   APPARATUS.  9 1 

terior  ditto;  7,  Internal  carotid  artery,  with  the  two  curves  it  makes  in  the  caver- 
nous sinus;  8,  Internal  carotid  on  the  sides  of  the  pituitary  gland;  9,  Transverse 
reticulated  anastomosis  thrown  between  the  two  internal  carotids  behind  the 
pituitary  gland;  io.Bifurcation  of  Ithe  internal  carotid;  11,  11,  Posterior-cerebral 
arteries  anastomosing  behind  the  pisiform  tubercle,  receiving  in  the  middle  of 
this  anastomosis  the  two  terminal  branches  of  the  basilar  trunk;  12,  Middle  cere- 
bral artery;  13,  Anterior  cerebral  artery;  14,  Posterior  communicating  artery. 

Posterior  cerebellar,  to  lateral  and  posterior  borders  of  cerebel- 
lum. 

Anterior  cerebellar,  two  or  three  in  number.  To  anterior  por- 
tion of  cerebellum. 

Two  anastomosing  branches  with  internal  carotid..  They  are  not 
constant,  and  unite  with  carotids  at  second  curvature. 

Posterior  cerebral  are  given  off  from  the  basilar  terminal  branches, 
pass  outward  and  enter  Bichat's  fissure,  where  they  terminate 
in  the  choroid  plexus  or  on  the  surfaces  of  the  cerebrum  and 
cerebellum. 

Median  spinal  artery  passes  along  the  inferior  fissure  of  the 
cord  from  its  beginning  to  its  end.  It  receives  branches  from 
the  vertebral,  intercostal,  lumbar  and  sacral  arteries,  and  supplies 
the  cord  and  its  membranes. 

INTERNAL  CAROTID. 

Passes  up  to  base  of  skull  through  occipito-temporo-sphenoidal 
opening,  enters  the  cavernous  sinus,  has  two  curves  develop  in  its 
course;  in  the  second,  anastomosing  with  the  basilar.  They  com- 
municate with  each  other  by  a  transverse  branch,  pass  forward 
and  bifurcate  behind  the  optic  tract,  into  the  posterior  communi- 
cating and  the  common  trunk  of  the  anterior  and  middle  cere- 
brals. 

Posterior  communicating  passes  backward  beside  the  pituitary 
body  and  unites  with  the  posterior  cerebral. 

Middle  cerebral  passes  outward  into  Sylvian  fissure,  and  supplies 
the  brain  structure. 

Anterior  cerebral  passes  above  optic  commissure,  unites  with 
its  fellow,  curves  around  the  corpus  callosum,  runs  backward 
and  supplies  the  brain  structure.  It  anastomoses  with  post- 
cerebral  and  ophthalmic. 

EXTERNAL   CAROTID. 

Passes  forward  and  upward  to  great  branch  of  hyoid,  then  as- 
cends to  neck  of  condyle  of  lower  jaw,  where  it  bifurcates  into 
the  superficial  temporal  and  internal  maxillary. 


9  2  EQUINE  ANATOMY. 

Branches. 

A  few  to  the  guttural  pouch  and  parotid  gland. 

i.  Glosso-jacial  or  external  maxillary. 

Passes  downward,  forward  and  upward,  outside  of  lower  jaw 
in  front  of  masseter,  where  it  divides,  above  the  maxillary  spine, 
into  an  ascending  branch  to  the  nasal  muscles,  and  a  descending 
branch  to  the  nasal  openings. 

Branches. 

Pharyngeal,    to    soft    palate    and    pharynx. 

Lingual,  to  tongue. 

Sublingual,  to  sublingual  gland,  fraenum  linguae,  and  buccal 
mucous  membrane. 

Inferior  labial  or  coronary,  to  structures  of  lower  lip,  anasto- 
mosing with  opposite. 

Superior  labial,  to  upper  lip  and  nose. 

2.  Maxillo-muscular. 

To  pterygoid  and  masseter  muscles. 

3.  Posterior  auricular. 

To  external  ear,  to  parotid  and  middle  ear  by  stylo-mastoid 
foramen. 

4.  Superficial  temporal. 

Passes  upward  a  short  distance  and  divides  into  the  anterior 
auricular  and  sub-zygomatic.  The  former  supplies  the  external 
ear,  parotid  gland  and  temporal  muscle;  the  latter  passes  across 
face,  forming  the  transverse  facial,  and  ends  in  the  masseter  muscle. 

5.  Internal  maxillary. 

Passes  inward  along  the  outer  side  of  the  guttural  pouch,  enters 
the  sub-sphenoidal  foramen,  and  orbital  hiatus,  passes  through 
maxillary  hiatus  to  the  palatine  canal,  where  it  terminates  in  the 
palato-labial. 

In  the  first  or  buccal  part  it  gives  off  its  first  five  branches,  in 
its  second  or  sphenoidal  part  two,  and  four  from  its  third  or  infra- 
orbital part. 

Branches. 

1.  Inferior  dental,  through  inferior  dental  canal  to  lower  jaw 
and  teeth,  giving  off  mental  artery  at  the  foramen. 

2.  Pterygoid  vessels,  to  muscle. 

3.  Tympanic,  through   Glasserian  fissure  to  tympanic  cavity. 

4.  Spheno- spinous,  or  great  meningeal,  through  anterior  lacer- 
ated foramen  to  dura  mater. 


CIRCULATORY  APPARATUS.  93 

5.  Posterior  temporal,  to  muscle. 

6.  Deep  anterior  temporal,  to  temporal  fossa. 

7.  Ophthalmic,  passes  into  orbit,  then  out  of  it  by  the  orbital 
foramen,  and  divides  in  the  ethmoidal  fossa.  It  gives  off  muscu- 
lar and  ciliary  arteries  to  the  eye,  the  central  artery  of  the  retina, 
the  supra-orbital  to  the  forehead,  the  lachrymal  to  the  upper  lid 
and  gland,  cerebral  branches  to  the  anterior  lobes  of  the  brain, 
and  terminates  by  the  meningeal  branch  to  the  dura  and  a  nasal 
branch  to  the  ethmoid  and  median  septum. 

8.  Buccal,  to  superficial  and  deep  facial  muscles. 

9.  Staphylin,  to  soft  palate,   by  posterior  palatine  groove. 

10.  Superior  dental,  passes  through  superior  t  dental  canal  to 
infraorbital  foramen,  where  it  divides  into  one  small  branch  to  the 
face,  and  another  to  the  incisor,  canine  and  anterior  molar  teeth. 

11.  Nasal,  to  outer  and  inner  walls  of  nasal  cavity. 
Palato-labial,   passes   along   palatine   groove    to   near   central 

incisors,  then  up  through  the  incisive  foramen  to  the  nose  and 
structures  of  the  upper  lip  and  gum. 

POSTERIOR  AORTA. 

Passes  upward  and  backward  to  the  seventh  dorsal  vertebra, 
forming  its  arch,  thence  to  the  space  between  the  pillars  of  the 
diaphragm,  where  it  becomes  the  abdominal  aorta.  At  the  last 
intervertebral  articulation  it  ends  in  a  double  bifurcation,  the  two 
internal  and  two  external  iliac  arteries. 

THORACIC   AORTA. 

From   seventh  dorsal   to   pillars  of  diaphragm. 

Branches. 

Inter costals,  17,  the  first  from  the  cervical,  the  next  three  from 
dorsal,  and  remainder  from  aorta.  Divides  into  a  superior  branch 
to  muscles,  skin  and  cord,  and  an  inferior  or  intercostal  behind 
each  rib,  which  anastomoses  below  with  internal  mammary. 

Broncho-cesophageal. 

By  two  branches  to  bronchi  and  lungs,  by  two  to  oesophagus, 
and  small  branches  to  trachea,  glands  and  mediastinum. 

ABDOMINAL  AORTA. 

From  diaphragm  to  bifurcation. 

Branches. 

Phrenic,  two  or  three,  to  diaphragm. 


Fig.  13. 


Q4 


CIRCULATORY  APPARATUS.  95 

C celiac  axis. 

Below  preceding,  and  divides  after  one-half  of  an  inch,  into 
gastric,  hepatic  and  splenic. 

Gastric,  by  two  branches  to  stomach,  gullet  and  lung. 

Splenic,  passes  to  left  to  spleen,  and  gives  off  branches  to  spleen, 
stomach  and  left  gastro-omental. 

Hepatic,  passes  forward  and  to  right  to  liver  and  gives  off 

Pancreatic,  pyloric  and  right  gastro-omental  branches. 

GREAT  MESENTERIC. 

Arises  near  renal  vessels  two  inches  behind  the  preceding, 
passes  downward,  and  after  a  course  of  1^  inches  divides  into 
branches  to  small  intestine,  ilio-ccecal,  superior  and  inferior  cazcal, 
right  colic,  left  colic,  small  colic  and  some  twigs  to  supra-renal 
capsules,  mesentery,  etc. 

SMALL   MESENTERIC. 

Arises  four  to  six  inches  behind  preceding,  and  sends  branches 
to  the  small  colon  and  rectum. 

Renal,  two. 

Arise  near  great  mesenteric,  and  supply  the  kidneys  and  supra- 
renal glands. 

Spermatic,  two  in  number. 

In  the  male  are  called  great  testicular,  in  female  utero-ovarian. 
Arise  near  small  mesenteric  and  pass  through  inguinal  canal 
to  testicle,  in  the  female  to  the  ovaries  and  cornua  of  the  uterus. 

Small  testicular,   male;   uterine,   female.     Two  in  number. 

Arise  from  bifurcation  of  aorta  or  from  internal  iliacs,  to  sper- 
matic cord  in  male,  and  uterus  and  vagina  in  female. 

Lumbar,  five  or  six. 

DISTRIBUTION    OF   THE    EXTERNAL   AND    INTERNAL    ILIAC   ARTERIES    IN    THE   MARE. 

i,  Abdominal  aorta;  2,  Internal  iliac  artery;  3,  Common  origin  of  the  internal  pudic 
and  the  umbilical  arteries— the  latter  is  cut;  4.  Internal  pudic  artery;  5,  Vaginal 
artery;  6,  Lateral  sacral  artery;  7,  Origin  of  the  gluteal  artery,  which  springs  in 
this  instance  from  the  lateral  sacral,  a  circumstance  most  frequently  observed  in 
the  Ass;  8,  Origin  of  the  ilio-muscular  artery;  9,  Origin  of  the  iliaco-femoral 
artery;  10,  Obturator  artery;  11,  External  iliac  artery;  12,  Circumflex  iliac  artery, 
cut;  13,  Femoral  artery;  14,  Common  origin  of  the  deep  femoral  and  pre-pubic 
arteries;  15,  Origin  of  the  anterior  great  muscular  artery;  16,  Origin  of  the 
saphena  artery,  cut;  17,  Innominate  branch;  18,  Popliteal  artery;  19,  Femoro- 
popliteal;  20,  Satellite  artery  of  the  great  femoro-popliteal  nerve;  21,  Posterior 
tibial  artery;  22,  Its  communicating  branch  with  the  saphena;  23,  External  plan- 
tar artery;  24,  Satellite  artery  of  the  internal  plantar  nerve;  25,  Digital  artery. 


96  EQUINE   ANATOMY. 

Divide  into  superior  branch  to  lumbar  muscles,  cord,  and 
inferior  to  abdominal  and  psoas  muscles. 

Sacra  media. 

A  single  vessel  arising  at  bifurcation  of  aorta,  passes  along  in- 
ferior face  of  sacrum  and  gives  branches  to  parts  in  vicinity. 

INTERNAL  ILIAC. 

From  aorta  to  insertion  of  small  psoas,  dividing  into  obturator 
and  ilio-jemoral. 

Umbilical. 

A  cord  to  top  of  bladder,  giving  off  some  vesical  branches. 

Internal  pudic,  to  neck  of  bladder,  bulb  of  urethra,  prostate  and 
seminal  vesicles.     In  female  to  vagina  and  uterus. 

Lateral  sacral. 

Passes  backward  alongside  of  sacrum,  gives  off  middle  and 
lateral  coccygeal  and  ischiatic  branches. 

Ilio-lumbar,  to  sacro-iliac  joint  and  muscles. 

Gluteal,  emerges  from  pelvis  by  great  sciatic  notch,  and  sup- 
plies gluteal  muscles. 

Obturator,  emerges  from  pelvis  by  obturator  foramen,  and 
sends  branches  to  muscles,  bladder  and  the  artery  of  the  corpus 
cavernosum,  giving  off  the  posterior  dorsal  artery  of  the  penis. 

Ilio-jemoral. 

Passes  out  of  the  pelvis  with  the  iliacus  muscle,  and  ends  in  the 
muscles  of  the  thigh. 

EXTERNAL  ILIAC. 

From  end  of  aorta  to  Poupart's  ligament,  where  it  ends  in  the 
femoral.     The  vein  lies  to  the  inner  side. 

Branches. 

Small  testicular.     See  before. 

Circumflex  iliac,  passes  outward  and  divides  into  an  anterior 
branch  to  the  abdominal  muscles  and  a  posterior  to  the  iliac  mus- 
cles and  skin  of  thigh. 

FEMORAL. 

From  Poupart's  ligament  to  the  opening  in  the  great  adductor 
of  the  thigh,  where  it  becomes  the  popliteal. 

Branches. 

Prepubic,   lies  on  anterior  face   of   Poupart's  ligament,   and 


CIRCULATORY  APPARATUS.  97 

divides  into  the  posterior  abdominal  (epigastric),  which  passes 
forward  into  rectus  abdominis  muscle,  anastomosing  with  the 
anterior  abdominal  and  the  external  pudic,  which  passes  through 
the  inguinal  canal,  and  divides  into  a  subcutaneous  vessel  on  the 
abdomen,  and  the  anterior  dorsal  artery  of  the  penis.  In  the 
female  this  supplies  the  mammary  gland. 

Profunda,  passes  back  behind  adductors  and  supplies  muscles 
of  thigh  and  coxo-femoral  joint. 

Superficial  muscular,  to  anterior  crural  muscles. 

Small  muscular,  to  muscles,  irregular  in  distribution,  one  giving 
off  the  nutrient  vessel  to  femur,  the  largest  in  the  body. 

Saphena,  accompanies  the  saphena  vein  to  inner  side  of  leg, 
thigh,  and  back. 

POPLITEAL. 

From  opening  in  adductor  magnus,  passes  beneath  the  gastroc- 
nemii  and  popliteus,  and  bifurcates  at  the  tibio-fibular  arch  after 
a  course  of  eight  inches  into  the  anterior  and  posterior  tibials. 

Branches. 

Articular,  to  femoro-tibial  joint. 

Muscular,  to  muscles  of  ham;  one  follows  great  femoro-popli- 
teal  nerve. 

Femoro-popliteal,  passes  backward  and  supplies  muscles  and 
nerves. 

POSTERIOR  TIBIAL. 

From  end  of  popliteal  to  side  of  astragalus,  where  it  divides 
into  the  two  plantar  arteries. 

Branches. 

Muscular. 

Tarsal  articular. 

Nutrient  artery  to  tibia. 

Plantar,  lie  along  tendon  of  perforans,  and  end  at  the  suspen- 
sory ligament  of  the  fetlock,  anastomosing  with  the  perforating 
pedal;  forming  an  arch  which  gives  off  the  external  and  internal 
plantar  interosseous,  which  supply  the  metatarsal  region. 

ANTERIOR  TIBIAL. 

Along  front  of  tibia  to  tibio-tarsal  joint,  where  it  becomes  the 
pedal.  It  gives  off  muscular  branches  and  one  along  fibula,  the 
analogue  of  the  peroneal  of  man. 


g&  EQUINE  ANATOMY. 

PEDAL. 

Divides  opposite  the  second  tarsal  row  into  the  perforating 
pedal,  which  passes  between  cuboid  and  scaphoid  to  anastomose 
with  plantars  and  collateral  artery  of  the  cannon.  This  passes 
downward,  then  backward  between  external  and  middle  meta- 
tarsus, then  down  to  top  of  fetlock,  where  it  divides  into  the  two 
collateral  arteries  of  the  digits,  which  pass  downward  to  the 
basilar  process  of  the  pedal  bone,  dividing  into  the  plantar  and 
preplantar  ungual. 

Branches. 

To  upper  bones  of  digits,  joints,  tendons,  etc. 

To  plantar  cushion. 

Coronary  circle,  to  structures  around  os  coronae. 

Pre-plantar,  enter  foramina  in  os  pedis. 

Plantar,  passes  into  plantar  fissure,  plantar  canal  and  semi- 
lunar sinus,  uniting  with  opposite  to  form  the  semilunar  anas- 
tomosis. 

PULMONARY  ARTERY. 

Arises  from  right  ventricle,  passes  upward  and  backward  divid- 
ing into  two  branches,  which  enter  the  lungs  and  ramify  in  them. 
At  its  middle  is  a  fibrous  cord,  running  to  the  arch  of  the  aorta, 
the  remains  of  the  ductus  arteriosus  of  fcetal  life. 

The  artery  carries  venous  blood  to  the  lungs  for  oxygenation. 

THE  VEINS. 

The  veins  carry  venous  blood  from  the  periphery  to  the  heart, 
except  the  pulmonary,  that  carry  arterial  blood  to  the  left  heart. 
They  have  three  coats,  an  internal  serous,  middle  muscular  and 
external  fibrous.  In  the  lumen  of  the  veins  are  valves  with  their 
concavity  toward  and  their  convexity  away  from  the  heart.  They 
are  absent  in  the  pulmonary  and  portal  veins  and  vena  cava  and 
very  large  and  numerous  in  the  extremities. 

The  venae  comites  are  two  veins  accompanying  each  small 
artery;  the  larger  arteries  have  only  one. 

Coronary. 

Small  branches  and  great  coronary  empty  into  right  auricle 
after  receiving  the  bronchial  veins. 


CIRCULATORY   APPARATUS.  99 

ANTERIOR  VENA  CAVA. 

A  large  trunk  from  anterior  opening  of  thorax  to  right  auricle, 
formed  by  the  union  of  the  two  axillary  and  two  jugular  vessels. 

Branches  received. 

Internal  thoracic,  vertebral,  superior  cervical  and  dorsal  vein, 
accompanying  the  arteries  of  the  same  name. 

Great  vena  azygos,  from  first  lumbar  vertebrae  to  sixth  dorsal, 
through  aortic  opening  of  diaphragm,  and  enters  the  anterior 
cava,  often  receiving  the  lumbar  and  aortic  intercostals. 

JUGULAR  VEINS. 

Begin  behind  inferior  maxilla,  below  its  articulation,  by  the 
joining  of  the  superficial  temporal  and  internal  maxillary.  Passes 
down  to  entrance  of  chest,  the  two  uniting  and  forming  a  con- 
fluence, into  which  the  axillary  veins  empty.  It  is  separated, 
above  from  the  carotid  by  the  omo-hyoid;  in  the  lower  part  it  is 
in  direct  relation  to  the  vessel. 

Branches. 

Maxillo-muscular,  posterior  auricular,  occipital,  glos so- facial, 
thyroid,  cephalic  or  plat,  and  many  smaller  ones. 

SINUSES   OF  THE  DURA  MATER. 

Median,  from  crista  galli  to  torcular  Herophili. 

Cavernous,  from  alveolar  vein  in  front  to  lacerated  foramen  be- 
hind. 

Occipito-atloid,  about  base  of  skull,  entering  spinal  veins. 

Petrosal,  from  cavernous  to  sub-sphenoidal  conduit,  where  it 
empties  into  occipital. 

SPINAL  VEINS. 

Median  spinal,  which  gives  off  branches  to  the  vertebral,  inter- 
costal and  lumbar  veins. 

AXILLARY   VEINS. 

Formed  by  union  of  subscapular  and  humeral  near  scapulo- 
humeral articulation  and  empty  into  jugulars. 

VEINS   OF   ARM. 

Humeral,  with  artery  and  deep  branches^    ;     »  »" 
Subscapular,  Ur-iCin^  j  wfrh  preceding;  n  3 ," .  \  ^    [V 
Subcutaneous  thoracic  or  spur,  into  humeral. 


CIRCULATORY   APPARATUS.  IOI 

FOREARM. 

Anterior  and  posterior  radial,  ulnar,  median  ending  in  basilic, 
cephalic  or  plat,  and  subcutaneous  radial.  Into  these  empty  the 
veins  that  accompany  the  corresponding  small  arteries  of  the 
metacarpal  and  digital  regions. 

POSTERIOR  CAVA. 

Begins  at  entrance  of  pelvis  by  union  of  common  iliac  veins, 
passes  forward  and  to  right,  grooves  liver,  through  diaphragm, 
and  ends  at  the  right  auricle  of  heart. 
Branches. 

Phrenic,  3. 

Portal  vein. 

Formed  by  junction  of  small  mesenteric,  great  mesenteric  and 
splenic,  similar  to  the  same  arteries.  It  begins  near  the  great 
mesenteric  artery,  passes  through  the  pancreatic  ring,  and  divides 
in  the  great  posterior  fissure  of  the  liver  to  enter  its  structure. 

The  right  gastro-epiploic  vein  and  gastric  enter  the  cava  near 
the  posterior  fissure. 

Renal,  two,  similar  to  arteries;  left  is  longer. 


Fig.  14.— general  view  of  the  veins  in  the  horse. 

Anterior  vena  cava;  2,  2,  Posterior  vena  cava;  3,  Right  pelvi-crural  trunk,  divided 
at  the  ilio-sacral  articulation;  4,  Left  pelvi-crural  trunk;  5,  Femoral  vein;  6,  Ob- 
turator vein;  7,  Sub-sacral  vein;  8,  Left  testicular  vein;  9,  Posterior  abdominal 
vein;  10,  Renal  vein;  11,  n,  Ascending  branches  of  the  asternal  vein;  12,  Vena 
azygos,  with  its  intercostal  branches,  and  in  front  the  sub-dorsal  venous  branch, 
13;  14,  Oesophageal  vein;  15,  Dorsal,  or  dorso-muscular  vein;  16,  Cervical,  or 
cervico-muscular  vein;  17,  Vertebral  vein;  18,  Right  axillary  vein,  cut  at  the 
anterior  border  of  the  first  rib;  19,  Sub-sternal,  or  internal  mammary  vein;  20, 
Left  axillary  artery;  21,  Termination  of  the  left  cephalic  vein;  22,  Left  jugular; 
23,  Right  jugular;  24,  External  maxillary,  or  glosso-facial  vein;  25,  Coronary 
vein;  26,  Angular  vein  of  the  eye;  27,  Sub-zygomatic  vein;  28,  Posterior  auricu- 
lar vein;  29,  Maxillo-muscular  vein;  30,  Internal  metacarpal  vein;  31,  Median 
subcutaneous  vein;  32,  Radial  subcutaneous  vein;  33,  Posterior  radial  vein;  34, 
Basilic  vein;  35,  Plat,  or  cephalic  vein;  36,  Coronary  venous  plexus;  37.  Digital 
vein;  38,  Internal  metatarsal  vein;  39.  Anterior  root  of  the  internal  saphena 
vein;  40,  Posterior  root  of  ditto;  41,  Internal  saphena;  42,  Great  coronary  vein; 
43.  Small  mesaraic  vein;  44,  Different  branches  of  the  great  mesaraic  vein;  45, 
Trunk  of  the  vena  portae  in  its  sub-lumbar  portion,  lodged  in  the  pancreas;  46, 
The  same  in  the  posterior  fissure  of  the  liver;  below  it  is  seen  entering  the  sub- 
stance of  the  gland,— m,  Subscapular  hyoideus  muscle  cut  obliquely  in  the  direc- 
tion of  the  trachea;  p,  Cervical  panniculus  turned  down  to  expose  the  jugular 
channel;  o,  Right  auricle  of  the  heart;  a,  Posterior  aorta;  G,  Section  of  the  right 
lung;  f,  Left  lobe  of  the  liver  behind  the  section  of  the  diaphragm;  r,  Right 
kidney  carried  up  and  forward;  l,  Oesophagus;  v,  Bladder;  s,  Rectum;  t, 
Thoracic  duct;  t',  Termination  of  that  duct  in  the  confluent  of  the  jugulars. 


102  EQUINE   ANATOMY. 

Spermatic,  follow  the  artery  in  male  or  female. 

Lumbar,  follow  arteries. 

Common  iliacs. 

Unite  under  second  lumbar  body  to  form  cava. 

The  common  and  external  iliacs  follow  the  course  of  the  arteries 
and  receive  similar  branches. 

Femoral  vein  follows  artery,  as  does  the  popliteal,  anterior  and 
posterior  tibial. 

Internal  saphena. 

Superficial  in  position  from  metatarsal  veins,  passes  along  inner 
side  of  leg  and  thigh,  and  empties  into  femoral  or  external  pudic. 

External  saphena. 

Begins  outside  calx  and  ends  in  popliteal  vein. 

Metatarsal. 

Internal,  external  and  middle. 

Digital. 

As  in  anterior  limb. 

PULMONARY   VEINS. 

Are  four  to  eight  in  number  and  extend  from  root  of  lung  to 
the  left  auricle.  They  carry  arterial  blood  and  are  destitute  of 
valves. 

LYMPHATICS. 

The  lymphatics  are  vessels  with  very  thin  and  transparent  walls, 
found  all  over  the  body,  except  in  blood-vessels,  nervous  tissue, 
bone,  muscles,  eyeball,  cartilage,  tendons,  the  membranes  of 
ovum,  placenta,  umbilical  cord,  cuticle  or  hair.  They  possess 
nutrient  vessels,  no  nerves,  have  valves,  and  carry  lymph  or  chyle 
into  the  vascular  system. 

The  lymphatic  glands  are  small  ovoid  bodies  in  the  course  of 
lymph  channels;  they  exist  as  groups  in  the  sub-lumbar,  inguinal, 
popliteal,  iliac,  femoral,  pre-pectoral,  pharyngeal,  pr e- scapular , 
mediastinal  and  bronchial  regions. 

They  have  a  special  capsule  and  are  composed  of  reticular 
tissue.  The  lymphatics  break  up  into  smaller  ones  before  reach- 
ing the  gland,  called  the  afferent  vessels,  and  are  united  again  on 
the  opposite  side  as  the  efferent  vessels. 

THORACIC   DUCT. 

Receives  all  the  lymphatics  except  those  of  the  right  side,  of 


NERVOUS   SYSTEM. 


103 


the  head,  neck,  thorax  and  right  anterior  limb.  Begins  at  the 
first  lumbar  vertebra  as  a  cistern,  the  "  receptaculum  chyli. "  The 
duct  then  passes  forward  through  the  pillars  of  the  diaphragm  to 
the  sixth  dorsal  vertebra,  where  it  passes  to  the  left  and  empties, 
after  a  dilatation,  into  the  anterior  cava  at  the  junction  of  the 
jugulars. 

RIGHT   LYMPHATIC   DUCT. 

Opens  at  junction  of  jugulars  and  is  guarded  by  a  valve.  It  is 
about  two  inches  long  and  receives  all  the  lymphatics  that  do  not 
empty  into  the  great  duct. 

NERVOUS  SYSTEM. 

This  system  is  divided  into  the  cerebrospinal,  presiding  over 
animal  life,  and  sympathetic,  over  organic  life. 

It  is  composed  of  white  fibres,  gray  vesicles  in  a  stroma  of 
neuroglia  or  connective  tissue,  and  a  gelatinous  material  in  the 
sympathetic. 

The  white  nervous  tissue  is  composed  of  an  outer  envelope  or 
tubular  membrane,  a  middle  coat  called  the  white  substance  of 
Schwann,  and  a  central  portion  which  transmits  nervous  impulses, 
the  axis  cylinder.  Outside  a  nerve  which  comprises  a  number  of 
the  preceding  we  find  a  covering,  the  neurilemma;  sensory  nerves 
terminate  at  the  periphery  in  many  different  ways,  motor  nerves 
as  small  plexuses  on  the  muscle  cells. 

CEREBRO-SPINAL  SYSTEM. 

Consists  of  the  brain,  spinal  cord,  ganglia  and  nerves. 

SPINAL  CORD. 

The  portion  of  the  nervous  system  enclosed  in  the  spinal  canal 
and  extending  from  the  occipital  foramen  to  the  upper  third  of  the 
spinal  canal.  Its  weight  is  10J  ounces;  it  is  flattened  above  and 
below,  and  has  two  enlargements  in  its  course,  one  between  the 
fifth  cervical  and  second  dorsal,  the  brachial,  the  other  below,  the 
crural. 

The  structure  is  externally  white  matter,  internally  gray,  ar- 
ranged like  two  horns,  the  larger  ends  pointing  down  and  out,  not 


io4 


EQUINE   ANATOMY. 


reaching  the  surface;  the  smaller  look  upward  and  outward, 
reaching  the  surface.  The  two  horns  are  connected  by  a  trans- 
verse band,  called  the  commissure,  which  shows  in  its  middle  the 
central  canal  of  the  cord. 

Fissures. 

Running  the  whole  length  of  the  cord  above  and  below  are  two 
fissures;  the  superior  longitudinal  is  narrower  and  more  shallow 
than  the  inferior,  which  is  separated  from  the  gray  commissure 
by  a  white  band,  the  white  commissure. 

Fig.  is. 


SECTION   OF  THE    SPINAL   CORD   OF  THE   HORSE  AT   THE    LUMBAR    REGION;    MAGNIFIED 
TWO   DIAMETERS. 

i,  Superior  median  fissure;  2,  Inferior  median  fissure;  3.  3.  Superior  collateral  fis- 
sures; 4,  4,  Inferior  ditto;  5,  Gray  commissure;  6,  White  commissure;  7,  7,  Su- 
perior gray  cornua;  8,  8,  Inferior  gray  cornua;  9.  Central  canal. 


Columns. 

The  superior  column  lies  between  the  superior  fissure  and  su- 
perior or  sensory  nerve  roots. 

The  inferior,  between  the  inferior  fissure  and  the  inferior  or 
motor  roots. 

The  lateral  lies  between  the  two. 

Membranes. 

Dura  mater,  outer,  is  not  adherent  to  bony  canal. 

Arachnoid,  as  in  brain. 

Pia  muter,  passes  into  fissures  and  on  sides  has  festoons  at- 


NERVOUS   SYSTEM. 


I05 


tached  to  the  dura,  the  ligatnentum  dentata.    Its  posterior  ex- 
tremity forms  a  narrow  prolongation,  the  plum  terminale. 

BRAIN. 

This  is  the  central  portion  of  the  nervous  system,  situated  in 
the  cranial  cavity. 

Membranes. 

The  dura  mater,  externally  is  a  strong  fibrous  membrane, 
adherent  to  the  bony  walls,  giving  off  prolongations  into  the  brain 
and  forming  depressions  for  the  venous  sinuses  (see  Veins).  It 
also  is  prolonged  on  the  nerves.  The  prolongations  of  the  dura 
are  the  (A)  jalx  cerebri,  passing  between  the  two  hemispheres  of 
the  brain  and  attached  to  the  crista  galli.  It  contains  in  its  meshes 
small  tubercles,  the  pacchionian  bodies. 

(B)  Tentorium  cerebelli,  which  forms  a  horizontal  partition  be- 
tween the  cerebrum  and  cerebellum,  and  attached  to  the  parieto- 
temporal crest,  and  parietal  protuberance. 

(C)  Pituitary  fold,  circumscribes  the  sella  turcica  and  envelops 
the  pituitary  gland. 

The  arachnoid  is  the  middle  membrane,  composed  of  a  base- 
ment membrane,  attached  to  the  dura  externally  and  a  covering 
of  flattened  endothelium  internally.  It  is  not  properly  a  vascular 
membrane.  It  does  not  pass  into  the  fissures  or  convolutions, 
and  between  it  and  the  pia  is  a  space  filled  with  cerebro-spinal 
fluid,  the  sub-arachnoid  space. 

Pia  mater. 

The  most  internal  of  the  membranes;  is  of  thin  structure,  hold- 
ing in  its  meshes  a  large  number  of  blood-vessels  which  have  peri- 
vascular lymph  spaces  about  them.  The  pia  passes  into  all  the 
inequalities  of  the  surface  of  the  brain,  and  supplies  it  with  blood. 

Weight. 

In  the  horse,  22  ounces,  15  drachms;  ox,  16  ounces,  15  drachms. 

In  human  male,  49^  ounces. 

Parts  of  the  brain. 

Cerebrum,  or  large  brain;  cerebellum,  or  small  brain;  the.  isth- 
mus and  medulla  oblongata. 

Medulla  Oblongata. 

The  medulla  is  the  upper  expanded  portion  of  the  cord,  ending 
at  the  pons,  and  rests  on  the  basilar  process.     It  shows  the  su- 
8     . 


106  EQUINE   ANATOMY. 

perior  median  and  inferior  median  -fissures,  the  latter  separating 
to  form  the  fourth  ventricle,  the  point  of  divergence  being  called 
the  calamus  scriptorius. 

Columns. 

The  inferior  median  columns  are  continued  as  the  pyramids; 
outside  these  are  two  oblong  elevations  (the  olivary  bodies  of 
man),  in  front  of  which  arise  the  sixth,  and  behind,  the  twelfth 
nerves. 

The  superior  median  column  is  continued  in  the  medulla  as 
the  restiform  body. 

The  lateral  tracts  are  the  continuation  of  the  lateral  columns. 

The  Isthmus. 

Is  the  prolongation  of  the  medulla,  supporting  the  cerebellum, 
and  terminating  in  the  cerebrum.  Its  component  parts  are  the 
pons  Varolii  or  mesencephalon,  crura  cerebri  and  cerebelli,  valve 
of  Vieussens,  corpora  quadrigemina,  thalami  optici,  pineal  and  pitu- 
itary glands. 

Pons  varolii. 

The  pons  is  an  elevated  mass  of  white  transverse  fibres  thrown 
between  the  two  halves  of  the  cerebellum;  it  rests  in  a  depression 
on  the  basilar  process,  and  below  presents  a  longitudinal  median 
groove  for  the  basilar  artery  (see  Arteries).    The  crura  pass  above  it. 

Crura  cerebri. 

The  crura  are  two  white  bands  continuous  with  the  fibres  of 
the  medulla,  entering  the  hemispheres  of  the  cerebrum  in  front 
and  in  contact  with  the  optic  thalami  and  quadrate  bodies  above, 
the  pons  below.  In  front  they  pass  under  the  optic  tracts,  which 
here  unite  and  form  the  optic  commissure.  The  crura  also  sepa- 
rate anteriorly  to  enclose  the  corpus  albicans. 

Crura  cerebelli. 

The  cerebellar  crura  are  composed  of  three  fasciculi: — 

i.  Crus  cerebelli  ad  pontem — the  pons'  transverse  fibres. 

2.  Crus  ad  medullam — the  restiform  bodies  of  the  medulla. 

3.  Processus  e  cerebello  ad  testes;  or  anterior  crura  to  the  testes 
of  the  corpora  quadrigemina. 

The  valve  of  Vieussens  is  a  thin,  transverse  layer,  which  passes 
between  the  anterior  cerebellar  crura.  It  forms  part  of  the  roof 
of  the  fourth  ventricle. 

The   corpora    quadrigemina  are  four  small  bodies  which  lie 


NERVOUS   SYSTEM.  107 

above  the  crura  cerebri;  the  anterior  pair,  or  the  nates  are  gray; 
the  posterior,  or  testes,  are  white. 

The  optic  thalami  are  two  masses  of  gray  matter  placed  above 
the  crura  cerebri;  they  are  separated  by  a  deep  groove,  and  form 
the  sides  of  the  third  ventricle.  At  their  posterior  border  are 
found  two  projections,  the  external  and  internal  geniculate  bodies. 

The  pineal  gland  or  conarium  is  a  cone-shaped  body,  of  a  red- 
dish brown  color,  situated  in  front  of  the  testes,  with  two  peduncles 
passing  forward  on  the  inner  sides  of  the  optic  thalami.  It  is 
composed  of  amorphous  tissue,  holding  salts  of  lime,  etc. 

The  pituitary  gland  is  a  small,  circular  body  attached  by  the 
infundibulum  to  the  tuber  cinereum,  a  layer  of  gray  matter  in  the 
floor  of  the  third  ventricle.  It  has  no  cavity  or  definite  structure. 
(For  interior  of  isthmus  see   Ventricles.) 

Cerebellum. 

The  cerebellum  is  that  part  of  the  brain  situated  behind  and 
beneath  the  cerebrum,  above  the  isthmus  and  separated  from  the 
cerebrum  by  the  tentorium. 

It  is  divided  into  three  lobes  by  a  median  constriction,  which 
is  divided  into  the  superior  and  inferior  vermiform  processes. 

The  lateral  lobes  are  convex,  and  show  many  convolutions  or 
depressions. 

Structure. 

Gray  externally,  white  internally,  with  a  tree-like  arrangement 
called  the  arbor  vitoz. 

Cerebrum. 

The  cerebrum  is  composed  of  two  portions,  the  hemispheres 
elongated  antero-posteriorly,  separated  by  a  deep  fissure  running 
in  the  same  direction  and  united  by.  a  transverse  commissure — 
the  corpus  callosum. 

The  longitudinal  fissure. 

This  passes  antero-posteriorly,  separating  the  two  hemispheres, 
and  bounded  below  by  the  corpus  callosum.  Behind,  at  the  an- 
terior and  superior  portion  of  the  medulla,  it  changes  its  direction, 
transmits  the  velum  interpositum,  and  is  called  the  fissure  of 
Bichdt  or  transverse  fissure.  The  longitudinal  fissure  lodges 
vessels  and  the  falx  cerebri. 

The  fissure  of  Sylvius  is  a  transverse  depression  in  front  of  the 
mastoid  lobule,  lodging  the  middle  cerebral  artery. 


io8 


EQUINE   ANATOMY. 


Lobes. 

The  olfactory  or  ethmoid  is  a  detached  portion  lying  below  and 
in  front  of  the  anterior  portion  of  the  cerebrum.     It  arises  by  two 

Fig.  16. 


GENERAL   VIEW    OF   THE    BRAIN;    LOWER   SURFACE. 

i,  Olfactory  lobe;  2,  Cavity  of  the  olfactory  lobe;  3,  External  root  of  the  olfactory 
lobe;  4,  s,  Cerebral  hemispheres;  6,  Cerebellum;  7,  Optic  chiasma,  or  commis- 
sure; 8,  Pituitary  gland;  9,  Optic  nerves;  10,  Tuber  cinereum;  11,  Crus  cerebri; 
12,  Third  cranial  nerve;  13,  Fourth  nerve;  14,  Pons  Varolii;  is,  Fifth  nerve;  16, 
Sixth  nerve;  17,  Seventh  and  eighth  nerves;  18,  Medulla  oblongata,  the  number 
being  placed  on  the  olivary  body;  19,  Anterior  pyramid;  20,  Roots  of  ninth, 
tenth,  and  eleventh  nerves;  21,  Twelfth  nerve. 

roots,  one  from  the  outside  of  the  mastoid  lobe  and  one  near  the 
optic  chiasm.  The  enlargement  or  bulb  lies  on  the  ethmoidal 
fossa,  and  has  an  internal  cavity  communicating  with  the  lateral 
ventricle  (see  First  Nerve). 


NERVOUS    SYSTEM. 


109 


Mastoid  or  sphenoid  lobe  represents  the  middle  lobe  of  man;  its 
margins  form  the  transverse  fissure  and  fissure  of  Sylvius.  Its 
interior  forms  a  cavity,  the  reflexed  portion  of  the  lateral  ventricles. 
The  convolutions  of  the  brain  are  numerous  and  distinct,  but 
do  not  call  for  a  detailed  description. 

INTERIOR   OF  THE   BRAIN. 

The  corpus  callosum  is  the  transverse  commissure  between  the 
hemispheres  and  seen  on  separating  them.  On  its  top  are  seen 
the  nerves  of  Lancisi  running  on  its  long  axis.  Its  inferior  surface 
forms  the  roof  of  the  lateral  ventricles  separated  by  the  septum 
lucidum.  Its  sides  end  in  the  interior  of  its  hemispheres.  Its 
hinder  border  forms  the  splenium  (or  pad),  turns  forward  as  the 
genu  (or  knee),  and  is  continuous  with  the  fornix.  Its  anterior 
portion  ends  in  the  cerebral  substance. 

THE  VENTRICLES. 

These  are  cavities  in  the  interior  of  the  brain  as  follows — 

Lateral  Ventricles  (two,  below  the  callosum). 

Third  Ventricle,  between  the  thalami  optici. 

Fourth  Ventricle,  between  the  diverging  restiform  bodies  of 
medulla.  (The  cavity  between  the  lamellae  of  the  septum  lucidum, 
the  fifth  ventricle  of  man,  is  absent  in  the  horse.) 

LATERAL  VENTRICLES. 

Are  lined  by  a  serous  membrane,  the  "ependyma,"  and 
bounded — 

Above,  by  corpus  callosum. 

Below,  by  corpus  striatum,  fornix,  hippocampus,  and  choroid 
plexus. 

Internally,  by  septum  lucidum. 

Externally,  by  brain  structure. 

Anteriorly,  continued  into  cavity  of  olfactory  lobe. 

Posteriorly,  continued  downward  and  upward  into  the  mastoid 
lobe. 

It  communicates  below  and  in  front  by  two  openings,  the 
foramina  of  Monro,  with  the  third  ventricle. 

The  septum  lucidum  is  a  thin  partition  of  white  matter  between 
the  lateral  ventricles. 

The  fornix,  a  single  body  between  the  third  and  lateral  ventri- 
cles, is  continuous  behind  with  the  callosum.  It  is  composed  of 
white  matter,  terminating  behind  in  two  prolongations,  the  poste- 


IIO  EQUINE   ANATOMY. 

rior  pillars,  ending  in  the  hippocampus,  in  front  by  two  similar 
ones,  which  form  the  corpus  albicans.  They  form  the  anterior 
boundaries  of  the  joramina  of  Monro. 

The  hippocampi  are  nuclei  of  gray,  covered  with  white  matter, 
on  the  floor  of  the  lateral  ventricle.  They  are  formed  by  the 
bending  in  of  the  convolution  above  the  corpus  callosum  and 
present  a  flattened  border,  the  corpus  fimbriatum. 

The  corpus  striati  are  projections  on  the  floor  of  the  lateral 
ventricles,  of  gray  and  white  tissue  in  lamellae.  They  are  sepa- 
rated from  the  thalami  by  long  bands,  the  taznioz  semicirculares. 
They  are  divided  into  two  parts,  the  intra-ventricular  and  extra- 
ventricular  nuclei. 

The  choroid  plexus  is  a  process  of  the  pia  that  passes  in  by  the 
great  transverse  fissure,  becomes  the  velum  interpositum,  passes 
from  the  lateral  to  the  third  ventricle  and  beneath  the  fornix. 
Their  veins  form  the  venoz  galeni,  which  end  in  the  sinus  of  the 
falx. 

THE  THIRD,    OR  VENTRICLE   OF   THE   THALAMI   OPTICI. 

Boundaries. 

Roof,  optic  thalami  meet  together. 

Floor,  lamina  cinerea. 

Sides,  optic  thalami  and  peduncles  of  pineal  gland. 

Communications . 

In  front,  foramen  of  Monro  with  lateral  ventricles. 

Behind,  the  iter  a  tertio  ad  quartum  ventriculum,  or  aqueduct 
of  Sylvius,  passing  under  the  corpora  quadrigemina  to  end  in  the 
fourth  ventricle. 

Running  across  the  cavity  are  also  seen  the  anterior  white  com- 
missure between  the  corpora  striata,  and  the  posterior  white 
commissure  between  the  thalami,  behind.  The  gray  commissure 
is  simply  the  coming  together  of  the  thalami  forming  the  roof. 

THE  FOURTH,  OR  CEREBELLAR  VENTRICLE  (see  Medulla). 

Boundaries. 

Roof,  valve  of  Vieussens  and  cerebellum. 

Floor,  medulla  and  pons. 

Sides,  restiform  body  and  processus  e  cerebello  ad  medullam. 

Anteriorly,  continuous  with  aqueduct  of  Sylvius. 

Posteriorly,  summit  of  calamus  scriptorius. 


NERVOUS   SYSTEM.  Ill 

Structure  of  the  Brain. 

Gray  structure  externally  and  dipping  down  into  the  convolu- 
tions.    There  are  seven  layers  in  the  cortical  substance  (Kolliker). 

The  white  substance  is  found  internally  and  runs,  as  fibres,  in 
various  directions. 

THE  CRANIAL  NERVES. 

There  are  twelve  in  number  (Sommering). 
ist,  or  Olfactory.     Nerve  of  smell  (see  Smell). 

Superficial    Origin. — See    Olfactory   lobe. 

Deep  Origin. — Corpus  striatum  and  transverse  fibres  of  pons. 

Exit. — Through  cribriform  plate  of  ethmoid. 

Distribution. — To  nasal  septum  and  ethmoidal  cells  in  upper 
third  of  nasal  fossae. 

Function. — Well  marked  and  presides  over  sense  of  smell. 
2d,  or  Optic. 

Origin. — From  commissure  and  optic  tracts  which  arise  from 
thalamus  and  corpora  quadrigemina. 

Exit. — Optic  foramen. 

Distribution. — To  retina  (see  Eye). 

Function. — Nerve  of  sight. 
3d,  or  Oculo-motor. 

Superficial  Origin. — From  crura  near  to  interpeduncular  fissure. 

Deep  Origin. — Anterior  border  of  pons. 

Exit. — Smallest  supra-sphenoidal  foramen  of  orbit. 

Distribution. — To  all  muscles  of  eye  except  external  rectus, 
great  oblique  and  part  of  the  posterior  rectus,  and  by  ophthalmic 
ganglion  to  the  iris. 
4th,  or  Patheticus. 

Superficial  Origin. — Band  of  Reil  behind  corpora  quadrigemina. 

Deep  Origin. — From  interior  isthmus. 

Exit. — By  smallest  supra-sphenoidal  foramen  to  orbit. 

Distribution. — To  great  oblique  muscle. 
5th,  or  Trifacial. 

Superficial  Origin.— By  two  roots,  the  larger,  or  sensory,  from 
the  sides  of  the  pons,  the  motor  from  pons,  near  the  other. 

Deep  Origin.— Sensory  root  from  restiform  body  of  medulla, 
the  interior  cells  of  the  isthmus  and  nuclei  of  other  nerves.  Motor 
root  from  antero-lateral  fasciculus  of  medulla. 


112  EQUINE  ANATOMY. 

Course. — Has  a  large  ganglion  developed  on  the  sensory  root, 
the  Gasserian,  resting  on  the  cartilage  of  the  occipito-spheno- 
temporal  hiatus,  and  divides  into  the  (i)  ophthalmic,  (2)  superior 
maxillary  and  (3)  inferior  maxillary  divisions. 

Exit. — The  first  branch  passes  through  the  smallest  of  the  large 
supra-sphenoidal  foramina  to  the  orbit.  The  second  passes 
through  the  foramen  rotundum  to  the  orbit.  The  third  passes 
through  the  foramen  ovale  to  the  temporo-maxillary  articulations. 

1.  Ophthalmic  Nerve. — To  skin  of  forehead,  eyelid,  lachrymal 
gland  and  nasal  fossa. 

2.  Superior  Maxillary. — Passes  along  infra-orbital  canal,  where 
it  ends  in  small  branches  to  the  face  and  upper  lip.  It  sends 
branches  to  the  eyeball,  palate,  nose  and  teeth  of  the  upper  jaw. 

3.  Inferior  Maxillary. — The  motor  root  unites  with  this,  passes 
down,  enters  inferior  dental  canal,  supplies  the  muscles  of  masti- 
cation, teeth  of  lower  jaw. 

Branches  are — 

Muscular  superficial,  temporal,  gustatory,  to  tongue,  mylo-hyoid 
and  mental. 

Sympathetic  Ganglia  of  Fifth. 

OPHTHALMIC   OR  CILIARY. 

Situation. — Near  nerve  to  inferior  oblique  muscle  of  orbit. 

Motor  Root. — From  third. 

Sensory  Root. — Nasal  branch  of  ophthalmic. 

-Sympathetic  Root. — Cavernous  plexus. 

Distribution. — Ciliary  nerves  to  iris. 

SPHENO-PALATINE   OR  MECKEL'S. 

Situation. — In  space  between  orbit  and  foramen  rotundum. 

Motor  Root. — Vidian  nerve  of  seventh. 

Sensory  Root. — Superior  maxillary. 

Sympathetic  Root. — Cavernous  plexus  by  Vidian. 

Distribution. — To  orbit  and  palate. 

OTIC   OR   ARNOLD'S. 

Situation. — Near  origin  of  inferior  maxillary  nerve  and  Eusta- 
chian tube. 

Motor  Root. — Small  petrosal  from  seventh. 


NERVOUS   SYSTEM. 


"3 


Sensory  Root. — Buccal  nerve. 

Sympathetic  Root. — From,  plexus  on  inferior  maxillary  artery. 
Distribution. — To  tensor  palati,   tensor  tympani,   Eustachian 
tube  and  pterygoid  muscles. 

6th,  or  Abducens. 

Superficial  Origin. — From  medulla,  behind  pons. 
Deep   Origin. — From   inferior   pyramid   and  lateral   tract   of 
medulla. 

Exit. — With  ophthalmic  branch  of  fifth. 
Distribution. — To  external  rectus  muscle  of  eye. 

7th,  or  Facial. 

Superficial  Origin. — From  medulla,  behind  pons. 

Deep  Origin. — Floor  of  fourth  ventricle. 

Exit. — Through  internal  auditory  meatus  with  eighth;  enters 
the  aqueduct  of  Fallopius;  has  a  ganglion  developed  on  it,  the 
geniculate;  passes  out  of  the  stylo-mastoid  foramen  to  the  muscles 
of  face  and  subcutaneous  of  neck. 

Branches. 

Great  petrosal,  to  Meckel's  ganglion. 
Small  petrosal,  to  otic. 
Tympanic,  to  stapedius. 
Chorda  tympani,  to  tongue  and  mouth. 

Muscular,  to  occipito-styloid,  digastric,  stylo-hyoid  and  subcu- 
taneous muscle  of  neck. 
Auricular,  to  ear  and  face. 

8th,  or  Auditory. 

Superficial  Origin. — Restiform  body. 

Deep  Origin. — Below  seventh. 

Exit. — With  seventh,  by  cochlear  and  vestibular  branches  to  ear. 

9th,  or  Glossopharyngeal. 

Superficial  Origin. — Medulla,  below  eighth. 
Deep  Origin. — Floor  of  fourth  ventricle. 
Exit. — By  posterior  foramen  lacerum  to  back  part  of  tongue 
and  pharynx. 

Branches. 

Jacobson's  nerve  (tympanic),  carotid. 
Communicating  with  sympathetic,  pharyngeal. 


114  EQUINE  ANATOMY. 

ioth,  or  Pneumogastric. 

Superficial  Origin. — Anterolateral  tract  of  medulla. 
Deep  Origin. — Floor  of  fourth  ventricle. 
Exit. — By  posterior  lacerated  foramen,  above  carotid  artery,  to 
front  of  thorax,  dividing  into  bronchial  and  oesophageal. 

Branches. 

Communicating  to  eleventh,  superior  and  inferior  cervical 
ganglia. 

Superior  laryngeal,  to  mucous  membrane  of  larynx  and  crico- 
thyroid muscle. 

Inferior  laryngeal,  to  all  muscles  of  larynx  except  crico-thyroid. 

Bronchial,  to  bronchi  and  lungs. 

(Esophageal,  to  oesophagus,  stomach,  liver  and  solar  plexus. 

nth,  or  Spinal  Accessory. 

Superficial  Origin. — Lateral  tract  of  medulla,  along  whole 
cervical  region  of  cord. 

Deep  Origin. — Fourth  ventricle. 

Exit. — Up  through  foramen  magnum  and  foramen  lacerum  to 
neck,  and  follows  mastoideo-humeralis. 

Branches. 

To  cervical  sympathetic,  sterno-maxillaris,  mastoideo-humeralis, 
cervical  and  dorsal  trapezius  and  cervical  nerves. 

1 2th,  or  Hypoglossal. 

Superficial  Origin. — Side  of  medulla  near  inferior  spinal  roots. 
Deep  Origin. — From  fourth  ventricle. 
Exit. — Condyloid  foramen. 

Branches. 

To  muscles  of  tongue. 

SPINAL  NERVES. 

They  are  42  or  43  pairs  that  leave  the  spinal  canal  by  the 
intervertebral  foramina.  The  superior  or  sensory  roots  have  a 
ganglion  developed  on  them.  The  motor  and  sensory  roots  unite 
and  soon  after  divide  into  a  superior  branch  to  the  spinal  muscles 
and  integument,  and  an  inferior  to  the  lower  part  of  the  trunk 
and  extremities.  Their  relative  number  in  the  different  regions 
are — cervical,  8;  dorsal,  18;  lumbar,  6;  sacral,  5;  coccygeal,  6  or  7. 


NERVOUS   SYSTEM.  II5 

CERVICAL  NERVES. 

Eight  in  number.  Divided  into  superior  branches  which 
anastomose  freely,  forming  the  deep  cervical  plexus,  and  send  fila- 
ments to  muscles,  nerves  and  integument  of  sides  and  top  of 
neck.  The  inferior  branches  supply  the  structures  on  the  under 
side  of  the  neck,  forming  the  superficial  cervical  plexus,  and  the 
sixth,  seventh  and  eighth  form  a  portion  of  the  brachial  plexus. 

Branches. 

Phrenic  nerves,  from  the  fifth  and  sixth  cervical,  and  branch 
from  the  brachial  plexus,  pass  down  inside  thorax  to  front  of 
diaphragm,  which  they  supply. 

BRACHIAL  PLEXUS. 

A  large  fasciculus  of  nerves  which  supply  the  anterior  limb  and 
anterior  portion  of  the  chest  and  neck. 

Formation. — By  inferior  branches  of  sixth,  seventh,  and  eighth 
cervical  and  first  two  dorsal  nerves,  which  unite  and  subdivide 
opposite  the  scapulo-humeral  joint  into  branches  to  the  thorax 
and  anterior  extremity. 

Branches. 

Muscular,  to  angularis  scapulae,  rhomboideus,  latissimus  dorsi, 
teres  major,  subscapulars. 

Superior  thoracic  (or  external  respiratory  of  Bell),  to  serratus 
magnus. 

Pectoral  or  inferior  thoracic,  to  superficial  and  deep  pectorals. 

Subcutaneous  thoracic,  follows  spur  vein  and  supplies  pannicu- 
lus  carnosus  and  subcutaneous  muscles  of  neck. 

Circumflex,  to  abductors  of  limb,  teres  major,  levator  humeri, 
shoulder-joint  and  integument  about  shoulder. 

Super-scapular,  from  sixth  and  seventh  cervical  to  antea-  and 
postea-spinati. 

Musculo-cutaneous,  from  seventh  and  eighth,  crosses  axillary 
artery,  passes  down  front  of  arm  between  two  insertions  of  coraco- 
humeralis,  supplying  it  and  the  coraco-radialis. 

Radial  (largest  branch  of  plexus),  passes  down  parallel  with 
humeral  artery,  follows  short  flexor  of  forearm  and  radial  artery  to 
oblique  extensor  oj  metacarpus. 


n6 


EQUINE   ANATOMY. 
Fig.  17. 


NERVOUS   SYSTEM.  117 

Fig,  17.— nerves  of  the  digit. 

p,  Plantar  nerve;  b,  Median  branch;  c,  Anterior  branch;  d,  Digital  artery;  h,  In- 
constant division  given  off  to  the  cartilaginous  bulbs;  1,  1,  Branch  to  the  plantar 
cushion;  k,  Transverse  coronary  branch;  m,  Podophyllous  branch;  o,  Pre- 
plantar  branch;  q,  Descending  ramuscule  to  the  fissure  of  the  patilobes;  r,  Ra- 
muscules  accompanying  the  digital  artery  in  the  plantar  fissure;  v,  Vein  whose 
presence  is  not  constant,  and  which  sometimes  accompanies  the  plantar  nerve 
throughout  its  phlangeal  course. 


Branches. 

To  extensors  of  forearm,  metacarpus  and  digit,  and  external 
flexor  of  metacarpus,  and  sensation  to  integument  of  anti-branchial 
region. 

Ulnar,  passes  down  behind  humeral  artery  to  inner  side  of  elbow, 
follows  oblique  flexor  of  metacarpus  to  pisiform  bone,  where 
it  divides  into  the  cutaneous  to  skin  of  anti-brachial  carpal  and 
external  metacarpal  regions  and  external  plantar.  It  gives  off 
branches  in  its  course  to  long  extensor  of  forearm  and  pectorali, 
to  all  muscles  of  posterior  brachial  region,  except  external  and 
internal  flexors  of  metacarpus. 

Median,  arises  from  posterior  part  of  plexus  and  a  branch  from 
musculo-cutaneous,  passes  down  in  front  of  humeral  artery,  along 
inner  side  of  forearm,  then  lies  anteriorly  again  and  bifurcates  at 
lower  one-third  of  forearm  into  external  and  internal  plantar. 

Branches. 

To  flexors  of  forearm  and  subcutaneous  region  of  forearm.  The 
plantars  give  off  the  anterior,  middle  and  posterior  digital  at  the 
fetlock,  which  supply  the  phalangeal  region. 

LUMBOSACRAL  PLEXUS. 

Formed  by  last  two  lumbar  and  first  three  sacral  nerves. 
Divided  into  an  anterior  division  lying  under  the  psoas  parvus, 
and  a  posterior  behind  the  internal  iliac  artery.  The  anterior  is 
formed  by  the  last  two  lumbar,  and  gives  off  ilio-muscular  to 
iliacus  muscle. 

Crural  or  anterior  femoral,  to  muscles  of  thigh,  and  by  saphenous 
branches  to  skin  of  inner  side  of  thigh  and  leg. 

Obturator,  passes  out  of  oval  foramen  to  adductors  of  thigh, 
pectineus,  short  adductor  of  leg  and  obturator  extemus. 

The  posterior  is  formed  by  first  three  sacral,  and  gives  off 


Il8  EQUINE   ANATOMY. 

small  sciatic,  which  emerges  from  great  ischiatic  notch  and  divides 
into  anterior  gluteal,  to  middle  and  small  glutei,  tensor  vaginal 
femoris,  and  posterior  gluteal  to  glutei,  triceps  cruris  and  sensa- 
tion to  posterior  part  of  thigh. 

Great  sciatic  emerges  from  great  sciatic  opening,  passes  along 
posterior  part  of  thigh  on  adductors,  between  two  heads  of  gas- 
trocnemii,  along  inner  side  of  hock,  and  ends  in  external  and  in 
ternol  plantar s. 

Branches. 

Muscular  to  obturator  intemus,  gemelli,  quadratus  jemoris, 
triceps  cruris,  semi-tendinosus,  semi-membranosus,  great  adductor 
of  thigh,  and  posterior  tibial  muscles. 

External  popliteal  arises  near  gemelli  muscles,  passes  down- 
ward and  outward  to  upper  part  of  leg,  where  it  terminates  in  the 
musculo-cutaneous,  which  supplies  the  extensors  of  the  phalanges 
and  skin  of  metatarsal  region,  and  anterior  tibial,  which  lies  to 
outer  side  of  artery,  giving  off  muscular  and  cutaneous  branches. 

Branch. 

Peroneal-cutaneous,  with  external  saphenous  vein  to  skin  of 
leg. 

Plantar  nerves  pass  to  outer  and  inner  sides  of  metatarsus,  and 
are  distributed  like  the  analogous  structures  in  the  anterior  foot. 

DORSAL  NERVES. 

Divided  into  superior  branches,  which  supply  skin  and  muscles 
of  spinal  region,  and  inferior,  which  send  branches  down  into  the 
intercostal  spaces  to  muscles  of  chest,  by  first  seven  pairs,  and 
muscles  and  skin  of  abdomen  by  remainder.  In  the  middle  of 
their  course  they  give  off  a  cutaneous  branch,  which  supplies  the 
skin  and  cutaneous  muscles.  The  first  and  second  form  part  of 
the  brachial  plexus. 

THE  SYMPATHETIC  NERVOUS  SYSTEM. 

This  consists  of  two  long  cords. lying  under  the  spinal  column, 
from  the  head  to  the  tail,  probably  ending  in  a  ganglion  under 
the  coccygeal  vertebrae. 

In  its  course  are  many  ganglia,  which  are  composed  of  the 
gelatinous  fibres  of  Remak,  and  send   branches  to  the  cerebro- 


NERVOUS    SYSTEM. 


II9 


spinal  system,  viscera  and  blood-vessels,  forming  the  vasomotor 
system. 

The  system  is  divided  into  cephalic,  cervical,  dorsal,  lumbar 
and  sacral  portions. 

Cephalic  consists  of  three  ganglia  of  fifth  nerve  (see  same). 

Cervical,  two  ganglia. 

1.  One  Superior,  lying  in  front  of  atlas,  on  carotid. 

Branches. 

Communicating,  to  ninth,  tenth,  eleventh  and  twelfth  nerves, 
and  fifth  cervical. 

Carotid,  on  internal  carotid,  also  to  cavernous  sinus.  Vidian 
nerve  and  cephalic  ganglia. 

Inferior  carotid,  to  external  carotid,  guttural  pouch,  salivary 
glands  and  pharynx. 

2.  One  Inferior,  near  insertion  of  scaleni  on  first  rib. 
Communicating,  to  tenth  and  cervical  nerves. 

Cardiac  nerves,  5 ;  two  from  left  and  three  from  right,  to  heart, 
bronchi  and  lungs. 
Dorsal  consists  of  17  ganglia,  below  vertebro-costal  joints. 

Branches. 

Small  ones  to  chest  and  pleura. 

Great  splanchnic. 

From  the  sixth  to  fifteenth,  to  abdomen  through  arch  of  psoas 
parvus,  and  near  cceliac  axis,  and  ends  in  solar  plexus,  which  sends 
branches  to  stomach,  liver,  spleen,  intestine,  kidneys  and  their 
capsules. 

Lesser  splanchnic. 

From  fifteenth,  sixteenth  and  seventeenth,  to  solar  plexus,  to 
kidney  and  supra-renal  bodies. 

Lumbar,  six  in  number,  lie  on  psoas  parvus. 

Branches. 

Posterior  mesenteric  plexus,  to  small  colon  and  rectum. 
Spermatic  plexus,  to  spermatic  vessels. 
Pelvic  plexus,  to  pelvic  viscera. 

Sacral,  four  in  number  beneath  sacrum.  Small  branches  to 
sacral  regions  and  vessels, 


120  EQUINE  ANATOMY. 

VISCERAL  ANATOMY. 
DIGESTIVE  SYSTEM. 

The  digestive  system  is  that  part  in  which  the  great  processes 
of  digestion  and  absorption  take  place,  as  well  as  the  expulsion  of 
the  residue  after  the  latter. 

The  parts  included  are  named  from  before,  backward,  the 
mouth,  pharynx  and  oesophagus,  that  carryt  he  food  to  the  abdom- 
inal organs,  the  stomach  and  intestines. 

The  annexed  organs  are  the  salivary  glands  to  the  mouth,  the 
liver  and  pancreas  to  the  intestines. 

THE  MOUTH. 

The  mouth  is  a  cavity  between  the  two  jaws,  and  having  an 
anterior  opening  between  the  lips  and  a  posterior,  the  soft  palate 
separating  it  from  the  pharynx.  On  the  sides  are  the  cheeks; 
below,  the  tongue. 

Tongue. 

This  is  a  flattened  muscular  organ,  elongated  antero-posteriorly 
and  fixed  to  the  hyoid  and  inferior  maxilla.  It  presents  calyci- 
jorm  papillce  on  the  dorsum  near  the  base,  arranged  in  a  V  shape. 
At  the  apex  of  this  are  two  depressions,  the  foramina  cceca.  Fili- 
form papillce  at  the  middle  of  dorsum  of  tongue.  Fungiform 
papillce,  club-shaped,  on  posterior  \  of  dorsum.  A  fibrous  cord 
(the  cartilage  of  the  tongue),  3  or  4  inches  long,  under  the  mucous 
membrane. 

Muscles. 

Intrinsic,  of  vertical,  longitudinal  and  transverse  fibres.  Ex- 
trinsic, see  stylo- glossus,  hyo-glossus,  genio-glossus  and  hyo- 
glossus  minimus. 

Action. — See  Deglutition. 

Nerves. — Lingual,  ninth  and  twelfth. 

Blood  Supply. — Lingual  and  sublingual. 

Palate. 

See  Muscles. 

Blood  Supply. — Ascending  pharyngeal  and  internal  maxillary. 
Nerves. — From  superior  maxillary  and  Meckel's  ganglion  of  the 
fifth. 


VISCERAL   ANATOMY. 


121 


Teeth. 

They  are  passive  agents  in  mastication,  and  are  in  number  40 
in  the  male,  36  in  the  female— viz.,  in  each  jaw  6  incisors,  12  molars, 
in  male  two  canines  in  addition. 

Parts. 

Crown,  fang,  neck  and  dental  pulp. 

Structure. 

Ivory  or  dentine,  outside  of  pulp  cavity. 

Cement,  covering  the  dentine. 

Enamel,  covers  free  portion  of  tooth,  formed  of  small  rods. 

Incisors. 

Are  pyramidal,  flattened  from  before,  backward,  with  a  single 


Fig. 


Profile  of  the  upper  teeth  of  the  horse,  more  especially  intended  to 

show  the  molars;  the  fangs  have  been  exposed. 

a,  Molar  teeth;  b,  Supplementary  molar;  c,  Tusk;  d,  Incisors. 

fang;  they  are  called  in  each  half  of  a  jaw,  the  pincer,  interme, 
diate  and  lateral  from  within  outward. 

Canines,  fangs  or  tusks. 

Found  only  in  male,  between  the  incisors  and  molars,  the  space 
between  them  and  the  latter  is  called  the  bar.  They  are  pointed, 
have  a  single  fang  and  grow  but  once. 

Molars. 

The  crowns  are  flattened  and  undulated,  and  communicate 
with  the  interior  of  the  fangs,  which  are  at  first  hollow,  then  filled 
with  dentine. 


122  EQUINE   ANATOMY. 

The  fangs  are  three  in  number;  in  the  terminal  molars,  both 
above  and  below,  the  intermediate  four  in  the  upper  and  two  in 
the  lower. 

SALIVARY   GLANDS. 

These  secrete  saliva,  which  exerts  a  chemical  and  mechanical 
action  on  the  food  in  the  mouth,  into  which  the  secretion  is  poured. 

They  are  the  parotid,  sub-maxillary,  sublingual,  molar,  labial, 
lingual  and  palatine. 

The  parotid  lies  behind  the  angle  of  the  lower  jaw,  is  the  largest, 
and  its  duct   (Steno's)   opens  opposite  the  third  upper  molar. 

The  sub-maxillary,  lies  in  the  intermaxillary  space  outside  the 
larynx,  its  duct  (Wharton's)  opens  at  the  side  of  the  fraenum  on 
a  small  tubercle,  the  barb. 

The  sublingual  lies  in  the  intermaxillary  space,  under  the  tongue, 
its  ducts  (of  Rivinian),  15  to  20,  open  near  that  of  Wharton  on  a 
ridge. 

The  molar  are  two  on  each  side  opposite  the  molar  teeth. 

PHARYNX. 

The  pharynx  is  an  elongated  cavity  behind  and  above  the 
mouth  and  nasal  cavities. 

Coats. 

Muscular,  see  Muscles. 

Mucous  of  basement  membrane,  covered  above  with  ciliated 
and  below  with  flattened  epithelium. 

Openings,  7. 

In  jront  two  posterior  nares,  two  Eustachian  tubes,  and  isthmus 
of  the  fauces. 

Below,  the  tops  of  the  oesophagus  and  larynx. 

Vessels. — Pharyngeal  and  thyroidal  arteries. 

Nerves. — Ninth,  tenth  and  sympathetic. 

CESOPHAGUS. 

The  oesophagus  is  a  long,  narrow  muscular  canal  beginning  at 
the  pharynx,  passes  through  the  thorax,  deviating  to  the  left, 
channels  the  lungs,  passes  through  a  special  opening  in  the  dia- 
phragm, and  ends  in  the  cardiac  extremity  of  the  stomach. 

Coats. 

Muscular. — Superficial,  longitudinal  and  deep  circular  fibres, 
the  upper  half  are  striped,  the  remainder  unstriped. 


VISCERAL  ANATOMY.  1 23 

Mucous. — Has  flattened  epithelium  and  is  thrown  into  numerous 
and  marked  folds. 

Blood  Supply. — External  carotid,  bronchial  and  oesophageal. 
Nerve  Supply. — Tenth. 


ABDOMINAL  CAVITY. 

The  abdomen  is  that  part  of  the  great  cavity  of  the  trunk  be- 
hind the  diaphragm.  It  is  bounded  above  by  the  lumbar  and 
sacral  vertebrae,  laterally  and  below  by  the  abdominal  muscles, 
behind  by  the  pelvic  brim. 

Regions. 

(a)  Superior  or  sub-lumbar,  under  the  psoas  muscles  and  lum- 
bar vertebrae. 

(b)  Inferior,  from  xiphoid  cartilage  to  pubes,  and  includes 
recti  muscles  laterally.  It  is  divided  from  before,  backward,  into 
the  supra-sternal,  umbilical  and  pre-pubic  regions. 

(c)  Inguinal,  about  inguinal  canals. 

(d)  Lateral,  from  ribs  to  pelvis,  and  superior  border  of  small 
oblique  to  outer  border  of  rectus.  The  hypochondrium  is  that 
part  behind  the  costal  free  borders.  The  flank  is  that  part  cov- 
ered by  the  internal  oblique. 

(e)  Diaphragmatic  is  the  space  included  in  the  concavity  of 
the  diaphragm. 

(/)  Pelvic,  bounded  above  by  sacrum,  below  by  pubes,  ischium, 
and  obturator  internus,  laterally  by  the  os  innominati  and  sacro- 
ischiatic  ligaments.  Behind  are  placed  the  rectum  and  genito- 
urinary organs. 

STOMACH. 

The  stomach  is  a  muscular  organ,  situated  in  the  diaphrag- 
matic region,  in  whose  cavity  the  principal  acts  of  digestion  take 
place.  Its  capacity  is  3  to  3J  gallons,  its  weight  3  or  4  pounds. 
In  form  it  is  elongated,  often  constricted  in  the  middle,  and  pre- 
sents an  anterior  and  posterior  face,  a  great  curvature  below,  to 
which  is  attached  the  great  omentum,  a  lesser  curvature,  to  which 
is  attached  the  gastro-hepatic  omentum;  a  left  dilatation,  the  fun- 


124 


EQUINE   ANATOMY. 


dus,  a  cardiac  extremity  continuous  with  the  gullet,  and  a  pyloric 
extremity,  forming  a  species  of  valve  opening  into  the  duodenum. 

Coats. 

Serous. — Most  external,  from  the  peritoneum,  and  completely 
covering  the  viscus,  except  at  the  greater  and  lesser  curvatures. 


Fig.  19. 


STOMACH    OF   THE    HORSE. 

a,  Cardiac  extremity  of  the  oesophagus;  b,  Pyloric  ring. 

It  has  three  folds  derived  from  it,  the  cardiac  from  the  cardia  to 
the  diaphragm,  the  gastro-hepatic  from  lesser  curvature  to  trans- 
verse fissure  of  liver,  and  the  great  or  gastro-colic  omentum  from 
great  curvature  to  sub-lumbar  region,  end  of  large  and  beginning 
of  small  colon. 


VISCERAL   ANATOMY.  I  25 

Muscular. — Three  layers,  external,  over  right  sac  and  also  left 
one;  middle,  circular  over  whole  organ,  aggregated  at  the  pyloric 
orifice  to  form  the  pyloric  valve;  internal,  looped  around  left  sac. 

Mucous. — This  is  thrown  into  folds  in  the  right,  but  not  in  the 
left  sac.  It  has  a  muscular  layer,  the  muscularis  mucosa,  and  is 
covered  with  flattened  epithelium  in  the  left  and  cylindrical  in  the 
right  sac. 

Glands. 

Infrequent  on  left  side  and  like  those  of  oesophagus.  Common 
on  right  sac,  and  are  of  two  varieties. 

(a)  Peptic,  with  a  narrow  neck  opening  into  two  or  three  cul- 
de-sacs,  lined  with  rounded  epithelium  at  the  periphery  and 
small  cells  next  to  the  lumen.  The  neck  is  lined  with  cylindrical 
cells. 

(b)  Mucous,  similar  in  structure,  but  the  whole  gland  is  lined 
with  cylindrical  epithelium. 

Blood  Supply. — Gastric,  splenic,  pyloric,  oesophageal,  right  and 
left  gastro-epiploic  vessels. 

Nerves. — Tenth  and  solar  plexus. 

Intestines. 

The  terminal  portion  of  the  alimentary  system,  beginning  at  the 
pylorus,  ending  at  the  anus  by  the  rectum.  It  is  a  narrowed  tube, 
twisted  and  curved  upon  itself,  and  divided  into  small  and  large 
divisions.  Their  entire  length  is  about  98  feet — 72  feet  for  the 
small  and  26  for  the  large. 

SMALL   INTESTINES. 

These  begin  at  the  pylorus,  form  a  loop  over  the  base  of  the 
caecum,  turn  transversely  to  the  left,  then  form  numerous  folds, 
being  suspended  by  a  process  of  peritoneum,  the  mesentery,  finally 
terminating  in  the  caecum  at  the  right  hypochondrium. 

Length,  24  yards;  diameter,  1-1}  inches. 

Divisions. — Duodenum,  the  first  curved  portion. 
Jejunum  (empty),  the  greater  part. 
Ileum  (twisted),  the  terminal  portion. 

Coats,  from  without  inward,  are — 

Serous,  from  peritoneum,  covering  all  the  small  intestine  com- 
pletely, except  a  portion  of  the  duodenum. 


126 


EQUINE   ANATOMY. 


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VISCERAL   ANATOMY.  1 27 

Mucous. — Soft  and  covered  with  columnar  epithelium. 
Blood  Supply. — Great  mesenteric  and  cceliac  axis. 
Nerves. — From  solar  plexus. 

LARGE   INTESTINE. 

Twenty-six  feet  in  length,  and  consists  of  the  ccecurn,  large  colon, 
small  or  floating  colon,  and  rectum. 

C^CUM. 

An  elongated  sac,  three  feet  in  length,  with  a  capacity  of  7? 
gallons,  lying  in  the  right  hypochondrium.  Its  superior  extremity 
(or  crook)  lies  under  the  right  kidney,  and  shows  the  two  open- 
ings of  the  ileum  and  beginning  of  the  colon;  it  is  encircled  by 
the  curve  of  the  duodenum. 

Coats. 

Serous,  from  peritoneum. 

Muscular,  four  external  longitudinal  layers,  which  are  inserted 
into  the  circular,  forming  a  number  of  transverse  folds. 

Mucous,  thicker  than  small  intestine;  it  contains  no  Brunnerian 
glands  or  patches  of  Peyer. 

Muscular,  of  non-striated  fibres,  an  external  longitudinal,  and 
internal  circular  coat. 

Points  of  Interest. 

Valvulce  conniventes,  folds  of  mucous  membrane  with  fibrous 
tissue  between,  in  duodenal  portion,  to  retard  passage  of  food. 

Openings  of  bile  and  pancreatic  ducts,  or  a  common  orifice,  five 
to  eight  inches  from  pylorus,  and  a  separate  one  for  the  accessory 
pancreatic  duct. 

Villi,  elevations  which  allow  of  passage  of  food  principles  in 
absorption,   connected  with  lacteals. 

Brunnefs  glands,  found  in  the  duodenum;  are  racemose  in 
character,  with  a  short  duct.     They  secrete  intestinal  juice.^ 

Crypts  of  Lieberkuhn,  over  all  parts  of  membrane;  are  simply 
depressions  lined  with  columnar  epithelium. 

Solitary  glands  are  lymphoid  tissue  with  no  duct,  and  are  more 
abundant  in  the  large  intestine. 

Glands  of  Peyer  are  groups  of  the  preceding,  found  for  the 
most  part  in  the  ileum;  they  are  one  hundred  in  number;  the 
largest  are  ij  inch  square,  oval  in  shape,  and  situated  opposite 
the  mesenteric  attachment. 


128  EQUINE   ANATOMY. 

Blood  Supply. — Caecal  vessels. 
Nerves. — Sympathetic. 

Large  Colon. 

About  twelve  feet  long;  it  begins  at  the  caecum,  passes  forward, 
then  bends  backward  and  to  the  left,  forming  the  supra-sternal 
curvature,  lying  above  the  sternum,  then  backward,  turns  again, 
forming  pelvic  -flexure;  runs  forward  to  the  diaphragm,  forming  a 
flexure  of  the  same  name,  then  passes  back  with  first  portion,  ter- 
minating in  the  small  colon,  after  diminishing  in  calibre. 

Coats. 

Serous  does  not  completely  cover  it. 

Muscular  and  mucous  same  as  cozcum. 

Blood  Supply. — Colic  vessels. 

Nerves. — Sympathetic. 

Small  Colon. 

About  ten  feet  long  ending  in  the  rectum.     Has  two  longitudinal 
bands  of  fibres,  and  is  lodged  in  the  left  flank. 
Coats. 

Same  as  preceding. 

Interior  shows  folds  like  large  colon  which  mould  faeces. 
Vessels,  small  and  great  mesenteric. 

Rectum. 

About  two  feet  long,  from  the  pelvic  inlet  to  its  outlet,  ending 
in  the  anus. 

It  is  very  dilatable;  has  no  ridges,  and  is  in  relation  to  the  sacrum 
above  and  the  genito-urinary  organs  below.  The  suspensory 
ligaments  of  the  penis  form  a  ring  around  its  posterior  portion. 

Coats. 

Serous  is  incomplete  behind. 

The  other  coats  are  like  those  of  colon. 

Anus. 

The  posterior  opening  of  the  alimentary  canal;  is  situated  under 
the  base  of  the  tail.  It  receives  an  aggregation  of  the  circular 
fibres,  which  form  the  internal  sphincter. 

External  Sphincter  arises  from  the  base  of  the  tail,  includes 
anus,  and  ends  in  perineal  muscles. 

Action,  by  constant  tension,  keeping  anus  closed. 


VISCERAL   ANATOMY.  129 

Retractor  Ani  arises  from  the  sacro-ischiatic  ligament  and  is 
inserted  into  sides  of  rectum. 

Action,  pulls  rectum  forward  after  defecation. 

Liver. 

The  liver  is  situated  in  the  abdomen,  in  the  right  diaphragmatic 
region.  Its  weight  is  eleven  pounds.  It  has  anterior  and  pos- 
terior flattened  surfaces;  thick  at  its  centre,  thin  on  its  edges. 

Lobes. 

Left  (largest),  right,  Spigelian  and  middle. 

Fissures. 

(i)  A  deep  one  for  the  posterior  cava;  (2)  another  in  the  centre 
of  its  posterior  surface  for  the  portal  vein  and  vessels;  (3)  one 
for  the  oesophagus;  (4)  and  one  dividing  the  right  and  left  lobes. 

Ligaments. 

(a)  Anterior  or  coronary,  from  fissure  for  cava  to  phrenic  centre. 

(b)  Of  left  lobe,  from  left  lobe  to  side  of  oesophageal  orifice. 

(c)  Of  right  lobe,  from  lumbar  wall  to  right  lobe. 

(d)  Broad  or  suspensory,  from  middle  lobe  to  upper  part  of 
inferior  abdominal  wall. 

(e)  Round,  from  umbilicus  to  middle  lobe.  It  is  a  fibrous  cord, 
formed  by  the  obliterated  umbilical  vein. 

Structure. 

Serous  coat  externally,  covering  it  completely,  except  at  the 
anterior  and  posterior  fissures  and  forming  ligaments. 

Fibrous  (Glisson's  capsule),  enters  posterior  fissure  and  follows 
vessels,  after  forming  an  outer  envelope  for  the  whole  organ. 

Parenchyma  or  essential  secreting  portion,  consists  of: 

Lobules  (?V  to  y1^  inch  in  diameter),  which  comprise  liver  cells, 
polygonal  in  shape,  -5-^5-  to  -^is  inch  in  diameter,  with  one  or  two 
nuclei.     They  lie  in  a  network  of  small  vessels. 

Hepatic  ducts  begin  between  the  liver  cells,  enter  the  peri-lobular 
connective  tissue,  unite  with  others  getting  constantly  larger,  and 
finally,  by  several  branches  from  the  different  lobes,  form  the 
ductus  choledochus  or  great  bile-duct.  This  ascends  in  the  gastro- 
hepatic  omentum  to  the  duodenum,  which  it  penetrates  six  inches 
from  the  pylorus,  surrounded  by  a  circular  fold  of  mucous  mem- 


i3° 


EQUINE   ANATOMY. 


*      £ 


VISCERAL   ANATOMY. 


131 


brane,  the  ampulla  oj  Vater,  in  common  with  the  pancreatic  duct. 
The  horse  has  no  gall  bladder. 

Course  of  blood  through  the  liver. 

The  portal  vein  enters  the  posterior  fissure,  forming  inter- 
lobular veins;  these  form  a  network  of  veins  between  the  cells,  then 
uniting,  form  the  intra-lobular  or  central  vein. 

The  intra-lobular  unite  in  the  sub-lobular  vessels,  which  are 
quite  numerous,  ending  as  hepatic  veins  by  opening  into  the 
posterior  cava. 

Lymphatics. 

Follow  the  vessels  forming  lymph  spaces  which,  uniting,  end 
in  the  receptaculum. 

Arteries. 

Hepatic,  from  cceliac  axis,  ending  in  the  lobular  centres. 

Nerves. — Solar  plexus,  tenth  and  phrenic. 

PANCREAS. 

This  viscus  resembles  the  salivary  gland  in  structure,  is  situated 
in  the  sub-lumbar  region,  under  the  aorta  and  cava,  and  behind 
the  stomach  and  liver. 

Form,  elongated,  triangular  or  curved  on  itself. 

Weight,  seventeen  ounces. 

It  has  a  superior  and  inferior  surface,  an  anterior  and  posterior 
border,  a  right  extremity  or  head,  and  a  left  or  tail,  toward  the 
spleen.     The  posterior  border  is  notched  for  the  portal  vein. 

Structure. 

Like  the  salivary  glands,  though  its  epithelium  is  rounded,  not 
columnar. 

Ducts. 

Principal  (duct  of  Wirsung)  runs  along  nearer  anterior  border 
from  tail  to  head,  receives  a  number  of  branches,  and  opens  into 
duodenum  in  common  with  the  bile  duct.  The  accessory  duct 
opens  alone  after  receiving  several  branches. 

Vessels. — Hepatic  and  great  mesenteric. 

Nerves. — Solar  plexus. 


I32  EQUINE    ANATOMY. 

SPLEEN. 

This  is  not  properly  an  annexed  gland  of  digestion,  but  from 
its  position  it  is  discussed  in  this  section.  It  has  no  duct  and  is 
therefore,  a  ductless  gland. 

It  is  situated  in  the  diaphragmatic  and  left  hypochondriac 
regions,  and  suspended  from  the  sub-lumbar.  Its  shape  is  falci- 
form, and  directed  downward  and  backward. 

Weight,  thirty-two  ounces. 

It  has  an  external  convex  face,  an  internal  concave,  a  convex 
posterior  and  concave  and  sharp  anterior  border,  a  base  or  superior 
extremity,  and  a  point  or  inferior  extremity. 

Ligaments. 

Suspensory,  from  sub-lumbar  region  and  left  kidney  to  base. 
Gastro-splenic  omentum,   a  process  of  peritoneum  enveloping 
whole  organ  except  at  anterior  fissure. 

Structure. 

Serous  coat,  from  peritoneum,  most  external. 

Fibrous  coat,  thick  and  strong,  sending  prolongations  or  trabec- 
ular into  the  interior  which  support  the  splenic  pulp. 

Splenic  pulp,  reddish  material  which  fills  the  interior  of  the 
organ;  composed  of  pigment,  broken  down  corpuscles,  etc. 

Malpighian  corpuscles,  small  rounded  bodies  of  lymphoid 
structure  enveloped  by  the  outer  tunic  of  the  small  arteries.  They 
are  large  in  well  fed,  and  small  in  starved  animals. 

Vessels . — Splen  ic . 

Nerves. — Solar  plexus. 

THE   PERITONEUM. 

The  peritoneum  is  a  serous  membrane  with  a  visceral  and 
parietal  layer,  and  enveloping  nearly  all  the  organs  of  the  abdom- 
inal cavity  more  or  less  completely. 

Beginning  at  liver  it  forms  the  ligaments  already  described,  a 
fold,  the  gastro-hepatic  omentum,  which  separates,  to  enclose  the 
stomach,  and  sending  reflections  to  the  duodenum  and  caecum  on 
the  right,  and  the  spleen  on  the  left,  forming  the  gastro-splenic 
omentum.  Its  median  portion  descends  in  front  of  the  intestines, 
having  a  large  amount  of  fat  developed  in  its  structure,  the  great 


VISCERAL   ANATOMY. 


133 


omentum.  This  is  confounded  laterally  with  the  mesenteries  of 
the  colon. 

The  great  omentum  communicates  with  the  general  peritoneal 
cavity  behind  the  stomach  by  an  opening,  the  foramen  of  Winslow, 
bounded  by  the  vena  ported,  cava,  pancreas  and  lesser  curvature 
of  the  stomach. 

It  is  then  reflected  over  the  small  and  large  intestines,  forming 
their  mesenteries,  the  ligaments  of  the  bladder,  broad  ligaments 
of  the  uterus,  and  then  from  the  rectum  and  front  of  the  bladder 
is  reflected  to  the  superior  and  inferior  abdominal  wall,  forming 
the  parietal  layers.  The  inferior  abdominal  portion  continues 
forward  and  forms  the  suspensory  ligament  of  the  liver.  The 
superior  abdominal  portion  passes  beneath  the  kidney,  giving  it 
support,  and  after  forming  the  mesenteries  is  continued  to  the 
diaphragm,  as  the  upper  layer  of  the  suspensory  and  gastro- 
hepatic  ligaments. 

Structure. 

A  basement  membrane  covered  with  flattened  polygonal  en- 
dothelial cells. 

RESPIRATORY  SYSTEM. 

In  this  system,  the  great  process  of  oxygenation  of  the  blood 
takes  place,  as  well  as  the  throwing  off  of  excrementitious  sub- 
stances, viz.,  carbonic  acid  gas,  solids,  etc. 

The  air  passages  are  from  above,  downward,  the  nasal  fossa, 
larynx,  trachea,  bronchi  and  lungs. 

For  a  description  of  nasal  fossoz,  see  special  senses. 

LARYNX. 

The  larynx  is  a  cartilaginous  box,  being  the  organ  of  voice.  Its 
anterior  opening  is  at  the  bottom  of  the  pharynx,  its  posterior 
continuous  with  the  trachea. 

Structure. 

Five  cartilages,  twelve  muscles,  and  a  mucous  membrane. 

Cartilages. 

Thyroid,  cricoid  and  epiglottis,  single  ones  and  one  pair,  the 
arytenoids. 


134  EQUINE   ANATOMY. 

Thyroid. 

(Shield-like.)  Composed  of  two  portions  united  in  front  and 
above  to  form  its  body;  to  its  superior  part  the  epiglottis  is  attached. 
The  lateral  portions  have  an  external  surface,  covered  by  muscles; 
an  internal,  covered  by  mucous  membrane;  an  anterior  or  supe- 
rior border,  to  which  the  great  cornua  of  the  hyoid  and  the  thyro- 
hyoid membrane  is  attached;  a  posterior  border,  showing  in  front 
the  attachment  of  the  crico-thyroid  membrane,  and  behind  an 
articulating  facet  with  the  cricoid. 

Cricoid. 

(Like  a  ring.)  Shaped  like  a  seal  ring  with  the  seal  upward, 
and  shows  an  external  face,  smooth,  and  on  its  flattened  portion 
spaces  for  the  origin  of  the  posterior  crico-arytenoids,  outside 
these  the  articular  facets  for  the  thyroid;  an  internal  face,  covered 
by  mucous  membrane;  a  superior  border,  with  facets  for  the 
arytenoids  and  attachment  of  crico-thyroid  membrane;  an  infe- 
rior border,  responding  to  the  trachea. 

Epiglottis. 

A  soft,  flexible  lid  that  covers  the  entrance  to  the  larynx.  It 
has  an  anterior  face,  which  gives  attachment  to  the  hyo-epiglot- 
tideus;  a  posterior,  covered  by  mucous  membrane;  a  circumference 
and  base  attached  to  the  thyroid. 

Arytenoids  (two). 

(Like  a  pitcher.)  Are  situated  above  the  cricoid  and  near  the 
top  of  the  larynx.  They  are-  irregularly  quadrilateral  and  show 
an  internal  face  lined  with  mucous  membrane;  an  external,  giving' 
attachment  to  arytenoid,  thyro-arytenoid  and  lateral  cricoary- 
tenoid muscles;  a  superior  border,  united  with  the  opposite;  an 
inferior,  giving  attachment  to  the  vocal  cord;  an  anterior,  joining 
with  its  fellow  and  giving  the  pitcher  appearance;  a  posterior, 
which  articulates  with  cricoid. 
Articulations  of  Cartilages. 

Thyroid,  with  cornua  of  hyoid,  by  thyro-hyoid  ligament  and 
thyro-hyoid  membrane. 

Thyroid  with  cricoid. 

Capsular  ligaments  for   facets   and   crico-thyroid   membrane. 

Arytenoids  with  cricoid. 

By  capsular  ligaments  for  facets. 

Arytenoids  with  thyroid. 

By  vocal  cords,  a  pair  of  fibrous  bands  which  enclose  a  triangular 


VISCERAL  ANATOMY.  1 35 

space,  the  glottis,  attached  in  front  to  thyroid,  behind  to  ary- 
tenoids. 

Epiglottis  with  thyroid,  by  simple  ligamentous  bands. 

Epiglottis  with  arytenoids,  by  some  bands,  sometimes  called  the 
superior  or  false  vocal  cords;  they  contain  some  cartilaginous 
bodies  (of  Wrisberg). 

Fig.  22. 


POSTERO-LATERAL    VIEW   OF  THE    LARYNX. 

I,  Epiglottis;  2,  Arytenoid  cartilages;  3.  Thyroid  cartilage;  4,  Arytenoideus  muscle; 
5,  Crico-arytenoideus  lateralis;  6,  Thyro  arytenoideus;  7,  Crico-arytenoideus  pos- 
ticus; 8,  Crico-thyroideus;  9,  Ligament  between  the  cricoid  cartilage  and  first 
ring  of  trachea;  10,  11,  Infero-posterior  extremities  of  crico-thyroid  cartilages. 

Muscles. 

Thyro-hyoid. 

Origin. — Outer  surface  of  thyroid  cartilage. 

Insertion. — Whole  hyoid  cornua. 

Action. — Carries  larynx  forward  and  upward. 

Hyo-epiglottideus . 

Origin. — Body   of   hyoid. 

Insertion. — Superior  face  of  epiglottis. 

Action. — Restores  epiglottis  to  erect  position. 

Crico-thyroid. 

Origin. — External  face  of  cricoid. 


136  EQUINE   ANATOMY. 

Insertion. — Posterior  border  of  thyroid. 

Action. — Brings  two  cartilages  together. 

Posterior  crico-arytenoid. 

Origin. — Posterior  flattened  part  of  cricoid. 

Insertion. — Posterior  tubercle  of  arytenoid. 

Action. — Rotates  the  arytenoids  outward,  thus  separating  vocal 
cords. 

Lateral  crico-arytenoid. 

Origin. — Anterior  border  of  side  of  cricoid. 

Insertion. — Outside   the   preceding   on   tubercle   of   arytenoid. 

Action. — Antagonist  to  preceding,  approximating  cords. 

Thyro-arytenoid. 

Origin. — By  two  fasciculi,  near  angle  of  thyroid. 

Insertion. — Lies  on  vocal  cord,  to  external  crest  of  arytenoid 
and    muscles. 

Action. — Constrictor  and  regulator  of  tension  of  larynx. 

Arytenoid. 

Origin. — From  external  face  of  one  cartilage. 

Insertion. — Into  the  analogous  point  of  the  other. 

Action. — Brings  vocal  cords  in  apposition. 

Mucous  Membrane. 

Covered  by  flattened  epithelium  on  cords  and  glottis;  else- 
where is  ciliated. 

The  glands  are  racemose  and  numerous  posteriorly. 

Vessels. 

Laryngeal  arteries. 

Nerves. 

Superior  laryngeal  supplies  mucous  membrane  with  sensation 
and  crico-thyroid  muscle.  The  inferior  laryngeal  supplies  the 
remainder. 

In  the  mule  and  ass  there  exists  a  deep  depression,  the  suh- 
epiglottic  sinus,  capable  of  great  vibration. 

TRACHEA. 

This  is  a  long  tube  composed  of  about  fifty  cartilaginous  rings, 
beginning  at  the  cricoid  and  ending  at  the  right  side  of  the  pos- 
terior aorta  opposite  the  left  auricle  of  the  heart.  It  lies  under 
the  oesophagus  and  between  the  two  carotids  in  the'  neck.  At  its 
end  it  bifurcates  into  the  two  bronchi. 


VISCERAL   ANATOMY. 


137 


Fig.  23. 


THE    RESPIRATORY   ORGANS;    INFERIOR,   OR   FRONT   VIEW. 

Trachea;  2,  Jugular  vein;  3,  Great  rectus  anticus  muscle;  4.  Carotid  artery; 
S,  Longus  colli  muscle;  6,  Origin  of  the  common  carotids;  7,  Vertebral  artery; 
8,  Section  of  first  rib;  9,  Cephalic  trunk  of  right  axillary  artery;  10,  Anterior  lobe 
of  right  lung;  11,  Middle,  or  supplementary  lobe  of  ditto;  12,  Posterior  portion  or 
lobe  of  ditto;  13,  Heart;  14,  Cardiac  artery;  15,  Ventricular  branch  of  cardiac 
vein;  16,  OZsophagus. 


IO 


138  EQUINE   ANATOMY. 

Structure. 

The  catilaginous  rings  are  incomplete  above,  where  the  space 
is  filled  in  by  transverse  muscular  and  fibrous  bands.  The  rings 
are  united  by  fibrous  tissue  which  fills  the  intervening  space.  The 
last  ring  is  often  divided  into  two  segments  for  the  bronchi  by  a 
median  spur. 

Mucous  Membrane. 

Is  covered  by  ciliated  epithelium,  and  its  glands  are  very  num- 
erous posteriorly. 

Vessels. 

From  carotid  and  axillary. 

Nerves. 

From  recurrent  laryngeal. 

BRONCHI. 

The  right  and  lejt  primary  bronchi  are  the  continuation  of  the 
trachea,  enter  the  root  of  each  lung  with  the  bronchial  artery,  veins 
and  nerves.  They  then  subdivide  into  a  large  number  of  branches 
which  go  on  subdividing  further.  They  are  round,  composed  of 
cartilaginous  circles  joined  to  each  other  by  muscular  fibre.  The 
cartilages  and  muscles  disappear  when  the  tubes  become  small. 
The  mucous  membrane  is  much  more  sensitive  than  that  of  the 
trachea,  otherwise  like  it. 

Vessels. 

Bronchial. 

Nerves. 

From  sympathetic  and  tenth. 

THE   LUNGS 

Are  the  essential  organs  of  respiration,  situated  in  the  thorax  on 
either  side  of  the  heart  and  enveloped  by  a  serous  membrane — 
the  pleurae.  They  are  described  as  two  lungs,  the  right  and  left. 
Each  lung  is  cone-shaped  and  has  an  external  face  lying  against 
the  ribs;  an  internal,  forming  the  side  of  the  mediastinum,  which 
shows  notches  for  the  oesophagus  and  aorta;  the  root  of  the  lung, 
where  the  bronchi,  vessels  and  nerves  enter  its  structure,  and  the 
attachment  of  the  ligamentum  latum  pulmonis,  a  process  of  the 
pleura  passing  backward  to  the  diaphragm;  a  base,  concave  and 
in  contact  with  the  diaphragm;  it  shows  a  small  lobule  on  the  right 


VISCERAL  ANATOMY.  1 39 

side  which  represents  the  middle  lobe  of  man,  and  also  a  notch 
for  the  posterior  cava.  The  apex  or  summit  lies  behind  the  first 
rib  and  is  somewhat  detached,  forming  the  anterior  lobe.  Thus 
the  right  lung  has  three  lobes,  an  anterior,  middle  and  posterior, 
the  left  two,  an  anterior  and  posterior.  The  superior  border  lies 
near  the  vertebrae;  the  inferior  is  notched  deeply  for  the  heart. 

Structure. 

Serous  from  pleura.     (See  below.) 

Parenchyma. — This  is  rose-colored,  soft,  strong  and  elastic. 
It  is  divided  into  lobules,  each  of  which  receives  a  small  bronchus, 
and  is  further  subdivided  into  alveoli,  spaces  with  which  a  num- 
ber of  smaller  spaces  communicate,  the  air  cells.  The  walls  of  the 
air  cells  have  a  thin  basement  membrane,  covered  with  flattened 
epithelium  -j-gVfr  to  ^rVff  °f  an  mcn  m  diameter.  Between  the  air 
cells  is  yellow  elastic  connective  tissue. 

Vessels. 

The  vessels  are  derived  from  the  pulmonary  and  bronchial 
arteries  and  the  pulmonary  vein.  They  form  a  plexus  under  the 
walls  of  the  air  cells,  which  allows  the  passage  of  oxygen. 

Nerves. 

Tenth  and  sympathetic. 

THE  PLEURA. 

The  pleurae  are  two  shut  serous  sacs,  which  form  the  borders  of 
the  mediastinae,  or  space  in  centre  of  the  chest. 

Structure. 

Basement  membrane  covered  by  flattened  epithelium  and  lubri- 
cated by  a  serous  fluid. 

Attachment. 

It  is  attached  to  the  root  of  the  lung,  there  giving  off  the  liga- 
mentum  latum,  then  envelops  the  whole  lung,  forming  the  visceral 
layer.  It  then  passes  to  the  chest  wall,  forming  its  costal  portion, 
to  the  diaphragm,  and  at  its  middle  is  in  contact  with  that  of  the 
opposite  side,  forming  its  mediastinal  portion;  encloses  the  heart, 
and  divides  the  chest  into  the  anterior  and  posterior  mediastinal. 

Nerves. 

Diaphragmatic,  intercostal,  tenth  and  sympathetic. 

Vessels. 

Bronchial  and  intercostal, 


140  EQUINE   ANATOMY. 

THORAX. 

This  cavity  is  bounded  in  front  by  the  first  ribs  and  longus  colli, 
and  has  passing  through  this  opening  lymphatic  glands,  trachea, 
oesophagus,  axillary  and  carotid  vessels,  anterior  cava,  tenth,  sym- 
pathetic, inferior  laryngeal  and  phrenic  nerves;  behind,  by  the  dia- 
phragm; above,  the  vertebroz,  ribs,  longus  colli,  thoracic  duct,  aorta, 
vena  azygos  and  sympathetic;  below-,  by  sternum,  costal  cartilages 
and  the  triangularis  sterni;  laterally,  by  ribs  and  deep  intercostal 
muscles. 

The  contents  are  heart  and  great  vessels,  lungs,  oesophagus, 
trachea,  nerves,  thoracic  duct,  etc. 

THE   MEDIASTIN^). 

The  portion  of  the  thorax  in  front  of  the  heart  is  called  the  an- 
terior mediastinum,  that  behind,  the  posterior.  The  former  con- 
tains the  trachea,  oesophagus,  anterior  aorta  and  divisions,  anterior 
cava,  thoracic  duct,  tenth,  cardiac,  recurrent  and  phrenic  nerves, 
and  thymus  gland  in  young  animal. 

The  latter  contains  the  posterior  aorta,  vena  azygos,  thoracic 
duct,  oesophagus,  tenth  and  left  phrenic  nerves,  and  ligamentum 
latum. 

Ductless  Glands. 

Spleen,  see  Abdomen;  supra-renal  bodies,  see  Kidney;  pituitary 
gland,  see  Brain. 

THYROID   GLAND. 

The  thyroid  is  a  gland  lying  in  the  neck  under  the  first  two 
tracheal  rings,  composed  of  two  lateral  lobes,  a  right  and  left, 
united  by  a  median  portion,  the  isthmus. 

Structure. 

Fibrous  coat,  which  covers  it,  and  sends  in  prolongations,  as  in 
the  spleen. 

Parenchyma. — This  is  divided  into  lobules,  which  contain  round 
vesicles,  lined  with  polygonal  cells,  and  containing  albuminous 
matter. 

Vessels. 

Thyro-lary  ngeal . 

Nerves. 

First  and  second  cervical  and  sympathetic. 


VISCERAL  ANATOMY.  141 

THYMUS   GLAND. 

This  is  a  gland  lying  at  the  back  part  of  the  neck,  under  the 
trachea,  and  partly  within  the  thorax.  It  has  two  lateral  lobes  in 
contact  with  each  other,  and  is  only  found  in  the  fcetus  and  young 
animal. 

Structure. 

Of  lobules,  which  contain  spaces  filled  with  granular  matter. 

The  lymphatics  are  well  marked. 

URINARY  ORGANS. 

They  comprise  the  kidneys,  ureters,  bladder  and  urethra  (in  the 
male  this  is  also  genital). 

THE   KIDNEYS. 

The  essential  organs  of  the  urinary  system  are  two  in  number, 
situated  in  the  abdomen,  to  the  right  and  left  of  the  sub-lumbar 
region,  against  the  psoas  muscles.  The  peritoneum  passes  under 
them.  The  right  is  heart-shaped  and  more  anterior  than  the  left, 
which  is  bean-shaped. 

Weight. — Right,  twenty-seven  ounces;  left,  twenty-five. 

Each  kidney  has  a  superior  and  inferior  flattened  surface,  an 
external  convex  border  and  an  internal  concave  one,  which  is 
deeply  notched,  and  called  the  hilum.  The  hilum  lodges  the 
vessels,  nerves  and  beginning  of  the  ureter. 

Interior. 

A  section  shows  that  at  the  hilum  is  found  a  cavity,  called  the 
pelvis,  the  beginning  of  the  ureter,  elongated  from  before  back- 
ward. Opposite  this,  in  the  proper  tissue  of  the  kidney,  is  seen 
a  ridge,  on  which  empty  the  uriniferous  tubes.  The  pelvis  is 
lined  with  mucous  membrane. 

Structure. 

Fibrous  coat  or  capsule,,  most  external,  and  sending  prolonga- 
tions into  its  interior. 

Parenchyma. — Divided  into  an  external  or  cortical  and  internal 
or  medullary  layer.  The  cortical  layer  is  darker,  and  contains 
small,  round  bodies,  the  Malpighian  corpuscles.  The  medullary 
is  lighter,  and  contains  the  uriniferous  tubules.  There  is  also 
some  connective  tissue  supporting  the  tubes,  vessels,  etc. 


Fig 


VISCERAL   ANATOMY.  1 43 

Fig.  24.— superior   and    general   view  of  the  genito-urinary  apparatus  in 
the  male,  with  the  arteries. 

a,  Left  kidney;  b,  Right  kidney;  a,  b,  Ureters;  c,  c,  Supra-renal  capsules;  d,  Blad- 
der; e,  e,  Testicles;  e,  Head  of  the  epididymis;  ^  Tail  of  the  epididymis;  f,  Def- 
erent canal;  G,  Pelvic  dilatation  of  the  deferent  canal;  h,  Left  vesicula  seminales; 
the  right  has  been  removed,  along  with  the  deferent  canal  of  the  same  side  to 
show  the  insertion  of  the  ureters  into  the  bladder;  1,  Prostate;  j,  Cowper's 
glands;  k,  Membranous,  or  intra-pelvic  portion  of  the  urethral  canal;  l,  Its 
bulbous  portion;  M,  Cavernous  body  of  the  penis;  tn,  m,  Its  roots;  n,  Head  of  the 
penis.  1,  Abdominal  aorta;  2,  2,  Arteries  (renal)  giving  off  the  principal  capsular 
artery;  3,  Spermatic  artery;  4,  Common  origin  of  the  umbilical  and  arteries  of 
the  bulb;  5,  Umbilical  artery;  6,  Its  vesical  branch;  7,  Internal  artery  of  the 
bulb;  8,  Its  vesico-prostatic  branch. 


Malpighian  Bodies. 

These  are  small,  round  vesicles  found  in  the  cortex,  lined  with 
cylindrical  epithelium,  and  containing  a  tuft  of  blood  vessels  (the 
glomerulus),  also  covered  by  epithelium.  There  are  two  open- 
ings,— one,  the  beginning  of  the  uriniferous  tubule,  the  other 
opposite  it,  showing  the  entrance  of  a  small  artery  and  the  emer- 
gence of  a  vein,  which  afterward  forms  a  plexus  around  the  tube. 

Uriniferous  Tubes. 

These  are  small  canals  running  through  the  medullary  structure 
of  the  viscus,  beginning  at  the  Malpighian  corpuscle,  and  ending 
on  the  ridge  of  the  pelvis.  They  are  first  single,  but  soon  subdi- 
vide into  straight  tubules,  then  descend  into  the  medulla  as  the 
loop  0}  Henle,  in  a  U  shape,  turn  on  themselves  and  run  back  to 
the  cortex.  Then  dilating,  have  several  bends,  pass  down  again 
through  the  medulla,  narrow  and  empty  on  the  ridge  of  the  pelvis, 
as  the  convoluted  tube. 

Structure. 

Amorphous  basement  membrane  covered  with  flattened,  pol- 
ygonal or  polyhedral  epithelium  in  different  localities. 

Vessels. 

The  renal  artery  divides  into  several  which  give  off  branches  to 
cortex  and  medulla,  glomeruli  and  tubes. 

The  branches  to  the  medulla  descend  between  the  tubes. 

The  veins  of  the  capsule  are  collected  in  a  stellate  manner,  the 
stars  of  Verheyen.  They  also  form  arches  at  the  junction  of  the 
cortex  and  medulla,  and  finally  uniting  form  the  renal  vein. 

The  nerves  are  from  the  solar  plexus. 


144  EQUINE   ANATOMY. 

SUPRA-RENAL  CAPSULES. 

The  supra-renal  capsules  are  two  small  elongated  bodies  lying 
to  the  under  and  inner  side  of  the  pelvis  of  the  kidney. 

Form. — Elongated  and  flattened,  two  inches  long;  right  larger. 

Structure. 

External  fibrous  coat,  which  projects  inward,  forming  spaces. 

Parenchyma. 

(a)  Cortical  substance.  Dark-brown  in  color,  and  consists-  of 
granular  nucleated  cells. 

(b)  Medullary  substance.  Yellow  and  soft,  of  a  delicate  retic- 
ular structure  filled  with  cells  and  nerve  structures. 

Vessels. — Mesenteries  and  renal. 

Nerves. — In  large  numbers  from  solar  plexus. 

THE   URETERS. 

The  ureters  are  two  in  number,  beginning  at  the  pelvis  of  the 
kidney,  run  back  and  downward  to  the  superior  and  posterior 
portion  of  the  bladder,  where  they  penetrate  its  muscular  coat  for 
an  inch  before  opening  into  its  interior.  It  is  the  size  of  a  goose 
quill. 

Structure. 

External,  fibrous  layer;  middle,  of  external,  circular  and  inter- 
nal longitudinal  muscular  fibre,  and  an  internal,  mucous,  ridged 
in  its  long  axis,  and  covered  with  stratified  pavement  epithelium. 

THE  BLADDER. 

This  is  a  muscular  bag  in  which  the  urine  is  accumulated  before 
being  discharged  from  the  body.  It  occupies  the  inferior  part 
of  the  pelvic  cavity,  and  has  three  openings,  the  orifices  of  the 
two  ureters  and  beginning  of  the  urethra. 

Weight,  sixteen  ounces. 

Parts. 

Near  the  urethral  opening,  the  neck;  between  the  urethral 
opening  and  the  openings  of  the  two  ureters  a  triangular  space, 
the  trigone.  It  rests  by  its  inferior  surface,  or  base,  on  the  pubo- 
ischial  symphysis.  Its  anterior  extremity  or  fundus  is  in  relation 
to  the  large  colon.  Above,  it  is  in  relation  with  the  uterus  and 
vagina  in  the  female,  the  seminal  vesicles  and  rectum  in  the  male. 


VISCERAL  ANATOMY. 


145 


Coats. 

Peritoneal  or  serous  (external),  covers  only  its  anterior  half; 
passes  back  farther  superiorly.  Forms  three  ligaments,  one  an- 
terior, two  lateral. 

Muscular,  of  unstriped  tissue  of  longitudinal,  oblique  and  cir- 
cular fibres.     The  latter  very  marked  at  the  neck,  the  sphincter. 

Mucous. — Pale,  covered  with  stratified  and  flattened  epithelium, 
and  contains  simple  glands. 

Vessels. — Internal  pudic  and  umbilical. 

Nerves. — Pelvic  plexus  and  last  two  sacral. 

For  urethra  in  male,  see  Penis;  in  female,  see  External  Gen- 
itals. 

MALE  GENITAL  ORGANS. 

THE  TESTICLES. 

The  testicles  are  two  oval  tubular  glands  lying  on  either  side  of 
the  penis  and  enveloped  in  a  double  bag  of  the  abdominal  skin 
and  fascia,  the  scrotum. 

Coverings. 

1.  Scrotum,  of  skin,  with  many  sebaceous  glands. 

2.  Dartos,  two  pouches  of  contractile  tissue,  in  contact  in  the 
median  line,  the  septum  scroti. 

3.  Cremaster,  from  the  ilio-lumbar  aponeurosis  to  the  outer 
side  of  the  next  covering. 

4.  Fibrous  tunic  (infundibuliform  fascia),  covers  the  whole 
testis,  and  is  a  process  of  the  transversalis  fascia. 

5.  Tunica  vaginalis  is  a  short  serous  sac,  enveloping  each 
testicle,  derived  from  the  peritoneum.  It  forms  a  covering  for 
the  spermatic  cord,  and  below  is  divided  into  a  visceral  layer, 
covering  the  testicle  and  epididymis,  and  a  parietal  lying  inside  the 
fibrous  covering- 
Its  cavity  contains  some  fluid,  serous  in  character. 
Parenchyma. — This  consists  of  the  testis  proper  and  a  number 

of  seminal  tubes,  which  together  form  a  body  lying  on  top  of  the 
testis — the  epididymis. 

Fibrous  membrane  (or  tunica  albuginea)  is  a  strong  fibrous 
envelope,  which  sends  in  prolongations  or  trabecule  to  its  inte- 
rior, dividing  it  into  lobules.     At  its  upper  border  and  in  front 


146  "  EQUINE   ANATOMY. 

it  is  thickened,  and  called  the  corpus  highmorianum  or  mediasti- 
num testis:  through  this  the  seminal  tubules  pass  from  the  in- 
terior. 

The  tubules  are  divided  into  groups  or  lobules,  about  200  or  300 
in  number,  each  lobule  being  found  between  prolongations  of  the 
fibrous  tunic,  and  about  one  or  two  yards  in  length. 

The  tubules  are  about  ^io  °f  an  mcn  m  diameter;  have  a  base- 
ment membrane,  covered  by  several  layers  of  epithelium,  which 
fill  the  tube,  spermatozoids  being  found  in  the  lumen. 

The  lobuli  testis  consists  simply  of  these  tubes  much  convoluted; 
passing  through  the  mediastinum,  they  unite  in  about  twenty  tubes 
— the  vasa  recta;  forming  a  network,  the  rete  testis,  and  are  con- 
tinued into  the  epididymis  and  the  vasa  efjerentia. 

THE   EPIDIDYMIS. 

The  epididymis  is  an  elongated  body  lying  on  top  of  the  tes- 
ticle, and  composed  of  the  seminal  duct,  much  convoluted,  the 
vasa  efferentia  uniting  to  form  it  at  its  anterior  portion — the  head, 
or  globus  major.  The  posterior  extremity,  or  tail,  is  called  the 
globus  minor.  Between  the  globi  is  the  body.  The  seminal  duct, 
or  vas  deferens,  is  continuous  with  the  globus  minor. 

Structure. 

Externally  a  circular  and  longitudinal  muscular  layer,  with 
fibrous  covering,  covered  by  a  mucous  membrane  lined  with 
ciliated  epithelium. 

Arteries. 

Spermatic,  from  the  aorta. 

Veins  are  markedly  spread  out  on  the  cord,  the  pampiniform 
plexus,  which  finally  empties  into  the  posterior  cava. 

Nerves. 

From  sympathetic. 

Descent  of  the  Testis. 

The  testicle  remains  in  the  abdominal  cavity,  in  the  sub-lumbar 
region,  till  after  birth,  usually  reaching  the  scrotum  at  the  age  of 
six  months.  The  active  part  in  the  descent  is  taken  by  the  guber- 
naculum  testis,  a  fibrous  cord  continuous  below  with  the  dartos 
and  ending  above  in  the  abdominal  cavity.  It  pulls  the  testis  down- 
ward, carrying  the  peritoneum  before  it,  which  becomes  inverted 
over  it,  forming  the  tunica  vaginalis.     The  portion  at  the  upper 


VISCERAL  ANATOMY.  147 

part  of  the  scrotum  becomes  obliterated  and  cut  off  from  the  peri- 
toneal cavity. 

The  semen,  the  combined  secretion  of  the  testicles  and  glands 
of  the  urethral  canal,  is  a  white,  viscid,  alkaline  fluid,  holding  in 
solution  the  essential  elements  formed  by  the  testicles — the  sper- 
matozoa— which  are  elongated  bodies  g-^-  to  ¥^7  inch  long,  with 
an  oval  head  and  a  filamentous  tail. 

VAS   DEFERENS. 

This  is  an  elongated  canal,  as  large  as  a  goose  quill,  beginning 
at  the  epididymis  and  ending  at  the  seminal  reservoirs.  It  passes 
upward  through  the  inguinal  canal,  backward  into  the  pel- 
vis, crossing  the  ureters,  and  ends  by  uniting  with  the  vesicles  to 
form  the  ejaculatory  ducts. 

Structure. 

External,  fibrous  layer. 

Middle,  muscular,  of  two  longitudinal  and  one  circular,  layer. 

Internal,  mucous,  covered  with  columnar  epithelium. 

THE   VESICUL.E   SEMINALES. 

These  are  two  elongated  pouches,  which  store  up  the  semen 
for  the  copulative  act;  they  lie  above  the  bladder,  receiving  a 
peritoneal  fold.  They  have  a  body  and  an  anterior  and  posterior 
extremity.  Their  posterior  extremity  is  tapering  and  unites  with 
the  vas  to  form  the  ejaculatory  duct. 

Structure. 

1.  Serous  coat,  incomplete. 

2.  Fibrous. 

3.  Muscular,  like  bladder,  with  also  some  compressor  fibres  to 
evacuate  the  pouch. 

4.  Mucous  membrane,  continuous  with  ejaculatory  ducts, 
thrown  into  folds  with  numerous  glands,  which  furnish  a  part  of 
the  seminal  fluid. 

THE  EJACULATORY  DUCTS 

Are  two  very  short  canals  succeeding  the  vesicles,  and  formed 
by  their  junction  with  the  vasa  dejerentia.  They  pass  above  the 
prostate,  finally  emptying  into  the  urethra  on  either  side  of  an 
elevation,  the  veru  montanum.  In  front  of  this  is  the  opening 
which  runs  backward  into  the  sac  lying  between  the  vesicles  and 
inside  the  peritoneal  pouch.     The  opening  is  the  sinus  pocularis, 


148  EQUINE   ANATOMY. 

and  the  pouch  the  third  seminal  vesicle  (this  is  not  present  in  man 
to  nearly  the  same  extent). 

THE   PROSTATE   GLAND. 

The  prostate  is  situated  behind  the  neck  of  the  bladder,  and 
embraces  the  beginning  of  the  urethra,  being  divided  into  two 
lateral  lobes.  It  contains  a  number  of  conglomerate  glands, 
whose  secretion  is  poured  into  the  urethra  on  the  sides  of  the 
veru  monlanum.     It  also  contains  fibrous  structure. 

THE   URETHRA. 

This  is  an  elongated  canal  continuing  through  the  whole  penis, 
and  beginning  at  the  neck  of  the  bladder  as  the  meatus  intemus. 

It  "first  passes  backward,  curves  around  the  ischial  symphysis, 
and  then  downward  and  forward  in  the  structure  of  the  penis, 
between  the  two  corpora  cavernosa. 

Divisions. 

Prostatic  region,  dilated,  contains  veru  montanum,  sinus  pocu- 
laris,  and  openings  of  prostatic  glands. 

Membranous,  from  prostate  to  beginning  of  the  spongy  tissue 
(corpus  spongiosum). 

Spongy  or  extra  pelvic. 

Begins  near  exit  from  pelvis,  is  narrowed  and  terminates  on  the 
glans,  as  the  urethral  tube.  Just  before  this,  it  is  dilated,  the 
fossa  navicularis.  Behind  the  prostate  are  also  the  openings  of 
Cowpefs  glands. 

Structure. 

Mucous  membrane,  thin  and  covered  by  columnar  epithelium; 
in  some  parts  flattened. 

Erectile  tissue. 

Commences  at  ischial  symphysis  as  the  bulb,  spreading  out  in 
front  to  form  the  glans  penis,  into  which  the  cavernosa  are  in- 
serted. 

Its  structure  consists  of  fibrous  spaces  with  some  elastic  tissue, 
which  cause  erection  mechanically,  by  their  distention  with  blood. 
(For  muscles  see  Perineum.) 

cowper's  glands. 
These  are  two  in  number,  of  about  the  same  structure  as,  and 
smaller  than  the  prostate,  situated  near  the  outlet  of  the  pelvis,  on 
each  side  of  the  urethra,  and  throwing   their  secretion  into  it. 


VISCERAL  ANATOMY.  1 49 

PENIS. 

The  penis  is  the  organ  of  copulation,  attached  behind  to  the 
ischium  and  extending  forward  between  the  thighs,  under  the  ab- 
domen, where  it  ends  in  a  free  extremity,  the  glans,  the  anterior 
termination  of  the  spongy  body. 

It  consists  of  three  portions,  the  two  corpora  cavernosa,  between 
and  below  which  is  the  urethra,  enclosed  in  its  spongy  tissue. 
The  free  portion  is  lodged  in  the  sheath  or  prepuce. 

Urethra,  see  above. 

Corpora  Cavernosa. 

Are  divided  only  posteriorly  where  they  are  attached  to  the 
ischial  rami,  but  are  blended  in  front,  ending  by  entering  depres- 
sions in  the  glans.  Underneath  is  the  groove  which  lodges  the 
urethra. 

Structure. 

An  external  thick  fibrous  coat,  giving  off  a  median  prolongation, 
the  septum  pectini/orme,  which  separates  the  two  portions. 

The  interior  is  composed  of  cavernous  or  erectile  tissue  like  the 
spongiosum.  At  its  base  are  found  bouquet-shaped  arterial  tufts, 
called  arterice  hellicince. 

The  free  portion  of  the  penis  has  an  enlarged  base,  and  an  an- 
terior extremity,  the  glans,  which  is  rounded  and  limited  behind 
by  a  marked  elevation,  the  corona  glandis.  It  receives  behind 
the  insertion  of  the  corpus  cavernosum.  Below  this  the  urethral 
tube,  encircled  by  the  urethral  fossa;  under  this  a  marked  notch. 
The  glans  is  covered  by  a  dark  smooth  skin,  with  many  papillae. 

Suspensory  ligaments  of  penis  (2). 

Arise  beneath  sacrum,  pass  downward,  encircling  rectum,  and 
inserted  into  the  accelerator. 

Prepuce  or  sheath. 

A  fold  of  the  abdominal  integument  encircling  the  penis.  It 
contains  internally  a  number  of  sebaceous  glands.  It  has  in  its 
structure  two  fibrous  bands,  the  suspensory  ligaments  of  the 
prepuce. 

Blood  Supply. — Bulbo-urethral,  dorsal  arteries  and  of  corpora 
cavernosa. 

Nerves. — Internal  pudic  and  sympathetic. 


150  EQUINE   ANATOMY. 

THE   PERINEUM. 

The  perineum  is  the  space  lying  below  the  rectum,  and  on  the 
sides  of  the  external  genitals  in  both  sexes. 

Superficial  fascia. 

Arises  from  the  inner  sides  of  thighs.  Inserted  on  muscles  of 
perineum  and  sphincter  ani. 

Deep  fascia. 

Arises   from   ischial   tuberosities,   rectal   muscles   and   thighs. 

Inserted,  between  ischio-cavernosus  and  semi-membranosus, 
into  perineal  muscles  and  fascia. 

Muscles. 

(a)  Wilson's  muscle. 
Origin. — From  sides  of  pelvis. 

Insertion. — By  superior  and  inferior  fasciculi  into  urethra  in  its 
membranous  portion. 

(b)  Accelerator  urince. 

Origin. — From  under  surface  of  the  urethra. 
Inserted. — Into  top  of  urethra  often  passing  around  it;  extend- 
ing from  ischium  to  end  of  penis  by  transverse  fibres. 

(c)  Ischio-urethral  (compressor  urethrae). 
Origin. — From  ischial  arch. 

Insertion. — Into  lower  face  of  Cowper's  gland  and  Wilson's 
muscle. 

(d)  Transversus  perinei.    ' 
Origin. — Ischial  spine. 

Insertion. — Into  median  perineal  line. 
Action  of  Muscles. 

The  first  and  third  compress  the  urethra. 
The  second  acts  more  especially  in  emptying  it  of  urine,  or 
semen. 

The  fourth  dilates  the  urethra. 

FEMALE  GENITALS. 

THE   VULVA. 

The  external  orifice  of  the  female  genitals  is  situated  below  the 
anus  in  the  perineum.  It  is  a  slit-like  opening,  extending  verti- 
cally, terminated  above  and  below  in  the  superior  and  inferior 
commissures.     The  sides  are  formed  by  the  labice  (or  lips),  of 


VISCERAL  ANATOMY.  151 

skin  externally,  and  mucous  membrane  internally.     The  different 
structures  composing  it  are  the  clitoris,  urethra  and  hymen. 
The  Clitoris. 

This  is  a  body  two  or  three  inches  long;  lies  at  the  inferior 
commissure;  is  composed  of  erectile  tissue,  two  crura,  a  prepuce 
and  glans. 
The  Female  Urethra. 

Is  very  short,  and  opens  by  its  meatus  about  three  or  four 
inches  from  the  vulva  on  its  inferior  wall.  It  is  guarded  by  a 
mucous  valve  which  directs  the  urine  backward.  Its  calibre  is 
greater  than  in  the  male.  Its  coats  are  an  internal  mucous  and 
external  muscular,  of  circular  fibres. 
The  Hymen. 

Rare.     A  thin,  fibrous  structure,  shutting  off  the  vaginal  from 
the  vulvar  cavities.     It  is  perforated  by  several  openings. 
Structure  of  Vulva. 

Mucous  membrane,  with  many  mucous  and  sebaceous  glands. 

Bulb  0)  Vulva. — Consists  of  two  lateral  lobes  of  erectile  tissue, 
communicating  with  the  vessels  of  the  clitoris,  lying  on  either  side 
of  the  vulva. 
Muscles. 

Constrictor  vulva. 

Attachments. — Above  to  sacrum  and  sphincter,  and  below  to 
clitoris;  laterally  to  muscles  of  thigh. 

Action. — Constricts  vulvar  orifice. 

Constrictor  vagince. 

Attachments. — To  sides  of  rectum  and  vagina  at  junction  with 
vulva. 

Action. — Constricts  vagina. 

THE   VAGINA. 

The  vagina  is  a  long,  membranous  tube,  extending  from  the 
vulva  to  the  uterus,  and  serves  the  purposes  of  coition  and  passage 
of  the  foetus. 

Relations. 

Above,  rectum;  below,  bladder;  laterally,  ureters  and  con- 
nective-tissue. 

Structure. 

Inner  or  Mucous  Coat. — Pale;  a  basement  membrane,  covered 


152  EQUINE   ANATOMY. 

with  a  flattened  epithelium.  Is  covered  with  an  abundance  of 
mucus,  and  has  longitudinal  folds  (rugce). 

Outer  or  Muscular. — Of  circular  and  longitudinal  unstriped 
fibres. 

Serous  or  Peritoneal. — Only  in  its  anterior  part. 

Vessels. 

Internal  pudic. 

Nerves. 

Pelvic  plexus. 

THE   UTERUS. 

The  uterus  is  a  hollow,  muscular  organ,  in  which  the  ovum  is 
received,  and  the  foetus  developed.  It  is  situated  in  the  abdominal 
cavity  in  the  sub-lumbar  region,  its  posterior  extremity  ending 
in  the  pelvic  cavity. 

Relations. 

Above,  to  rectum;  below,  with  bladder;  anteriorly  and  laterally 
with  intestinal  convolutions;  behind,  with  vagina. 

Parts. 

Behind  is  a  constriction,  the  cervix  (or  neck),  with  a  circular 
opening,  the  os.  In  front  is  the  fundus,  directly  continuous  with 
the  two  cornua.  These  have  a  superior  or  convex,  and  posterior 
or  concave  curvature,  a  base  continuous  with  the  uterus,  and  a 
summit  continuous  with  the  oviducts. 

Ligaments. 

Two  broad,  descending  from  the  sub-lumbar  region  to  the  sides  of 
the  uterus  and  cornua  and  enveloping  the  ovaries  and  their  ducts. 

Two  rudimentary,  round  ligaments,  running  from  the  sides  of 
the  uterus  to  the  beginning  of  the  inguinal  canal. 

Structure. 

Serous  coat,  complete,  from  peritoneum. 

Muscular  coat,  longitudinal  (external)  and  circular  (deep) 
unstriped  fibres.     The  latter  most  marked  about  the  cervix. 

Some  muscular  fibres  pass  into  the  broad  ligaments. 

Mucous  coat,  of  basement  membrane  covered  with  ciliated 
epithelium,  except  at  the  cervical  canal,  where  it  is  columnar, 
and  at  the  os,  where  it  is  flattened.  It  is  thrown  into  folds  at  the 
cervix  and  is  divided  into  two  canals — those  of  the  cervix  and 
body.  It  is  supplied  with  mucus  by  numerous  simple  and  cylin- 
drical glands. 


VISCERAL  ANATOMY.  1 53 

Blood  Supply. 

Uterine  and  utero-ovarian  vessels. 

Nerves. 

Mesenteric  and  pelvic  plexuses. 

THE   OVIDUCTS,    OR   FALLOPIAN  TUBES. 

The  oviducts  are  two  tubes,  lying  on  either  side  of  the  uterus, 
in  the  broad  ligaments,  which  serve  for  the  passage  of  the  ovum 
from  the  ovary  to  the  uterine  cavity,  with  which  they  are  contin- 
uous, and  open  into  the  cornua,  by  a  narrowed  orifice  on  a  tuber- 
cle. In  its  middle  it  is  narrow,  and  at  its  ovarian  extremity  it  is 
dilated  and  divided  into  several  narrow  prolongations,  the  fim- 
briated extremity,  one  of  these  communicating  with  the  ovary. 

Structure. 
-    Serous  coat,  from  broad  ligament. 

Muscular,  of  circular  and  longitudinal  fibres. 

Mucous,  continuous  with  that  of  the  uterus,  covered  by  ciliated 
epithelium  and  thrown  into  longitudinal  folds. 

THE   OVARIES. 

The  ovaries  are  two  small  ovoid  bodies,  situated  in  the  sub- 
lumbar  region,  with  a  deep  notch  or  hilus  on  their  upper  surface 
which  receives  the  oviduct.  Into  this  the  ovum  is  discharged. 
It  is  attached  by  the  ovarian  ligament  to  the  uterus,  and  sup- 
ported by  the  broad  ligament. 

Structure. 

Serous  coat,  complete  except  at  hilus. 

Fibrous  coat  (or  tunica  albuginea),  very  strong. 

Stroma,  hard  and  grayish-red.  Is  divided  into  an  external 
cortical  and  internal  medullary  portion. 

Medulla,  red  and  spongy,   of  connective  tissue  and  vessels. 

Cortex,  of  connective  tissue,  holding  large  numbers  of  Graafian 
vesicles  or  ovisacs  which  contain  the  ova.  In  the  fully  formed 
state  they  project  on  the  surface  and  are  composed  of  a  tunica 
fibrosa,  tunica  granulosa  and  discus  proligerus,  a  collection  of 
cells  about  the  ovum. 


i54 


EQUINE    ANATOMY. 
Fig.  25. 


VISCERAL  ANATOMY.  1 55 

Fig.  25.— generative  organs  of  the  mare,  isolated  and  partly  opened. 

1,  Ovaries;  2,  2,  Fallopian  tubes;  3,  Pavilion  of  the  tube,  external  face;  4.  Ibid,  in- 
ner face,  showing  the  opening  in  the  middle;  5,  Ligament  of  the  ovary;  6,  Intact 
horn  of  the  uterus;  7,  A  horn  thrown  open;  8,  Body  of  the  uterus,  upper  face; 
9,  Broad  ligament;  10,  Cervix,  with  its  mucous  folds;  11,  Cul-de-sac  of  the  vagina: 
12,  Interior  of  the  vagina,  with  its  folds  of  mucous  membrane;  13,  Urinary 
meatus,  and  its  valve,  14;  15,  Mucous  fold,  a  vestige  of  the  hymen;  16,  Interior 
of  the  vulva;  17,  Clitoris;  18,  18,  Labia  of  the  vulva;  19,  Inferior  commissure  of 
the  vulva. 


Blood  Supply. 
Utero-ovarian. 
Nerve. 
Mesenteric  plexus. 

THE  MAMMARY   GLANDS. 

The  mammae  are  two  glandular  bodies  situated  in  the  posterior 
and  inferior  abdominal  region,  in  the  position  of  the  scrotum  in 
the  male.  They  are  hemispherical  in  shape,  terminating  below 
in  a  small  prominence,  the  nipple  or  teat. 

Structure. 

Skin,  of  abdominal  region,  thin  and  soft. 

Fibrous  coat,  of  elastic  fibrous  tissue,  which  sends  prolonga- 
tions into  its  interior. 

Parenchyma  of  vesicles  or  acini,  opening  into  lactiferous  ducts. 
These  unite  and  form  several  canals.  These  form  two,  three  or 
four  sinuses  opening  by  several  canals  on  the  nipple.  The  acini 
are  lined  with  polyhedral  epithelium  which  become  rounded  and 
fatty  in  lactation. 

Blood  Supply. 

External  pudic. 

Nerves. 

First  lumbar. 

ORGANS  OF  SPECIAL  SENSE. 
Smell. — Located  in  the  nasal  cavities. 

THE   NASAL  CAVITIES. 

Bony  walls. 
Floor. 

Two  superior  maxillary,  two  inter-maxillary  and  two  palate 
bones. 


156  EQUINE   ANATOMY. 

Roof. 

Nasal,  frontal,  ethmoid  and  sphenoid. 

Sides. 

Nasal,  inter-maxillary,  superior  maxillary,  palate  and  turbi- 
nated. 

Median  Septum. 

Perpendicular  plate  of  ethmoid,  vomer  and  mesial  cartilage. 
Openings  of  Communication. 

Anteriorly,  two  nostrils. 

Posteriorly,  two  posterior  nares,  with  pharynx. 

Laterally,  by  a  common  opening  into  the  middle  meatus,  the 
superior  maxillary,  sphenoidal,  ethmoidal  and  frontal  sinuses. 
The  inferior  maxillary  opens  alone. 

Above,  the  openings  of  the  cribriform  plate  transmitting  the 
olfactory  nerves. 

Below,  the  incisive  canal,  leading  to  the  mouth. 

THE   NOSTRILS, 

Are  the  two  oblong  openings  in  the  anterior  and  inferior  portion 
of  the  nose. 

Structure. 

Of  three  cartilages,  the  first  one  prolonged  from  the  tip  of  the 
nasal  bones,  two  lateral  cartilages  meeting  in  the  median  line  in 
an  x  shape  and  attached  at  the  side  to  the  inter-maxillary  bones 
by  a  broad  expanded  portion;  the  lower  extremity  forms  the 
curve  of  the  nostril. 

Muscles. 

Already  described. 

Skin. 

Thin  and  sensitive. 
Mucous  Membrane.- 

Covers  the  whole  surface  of  the  nasal  cavities  and  continued 
into  the  sinuses. 

Divided  into  two  portions.  The  olfactory  in  the  upper  one- 
third,  which  is  thin,  with  columnar  and  stratified  epithelium,  and 
the  cells  of  Schultze.  These  are  fusiform  in  shape,  with  a  deep 
prolongation,  continuous  with  the  olfactory  nerve,  and  a  super- 
ficial near  the  free  surface  of  the  membrane.  It  is  supplied  by 
the  first  nerve. 

The  Schneiderian  is  thick,  soft  and  spongy,  with  numerous 


VISCERAL   ANATOMY.  1 57 

vessels  and  glands.     The  epithelium  is  ciliated  and  supplied  by 
the  fifth  nerve  and  its  superior  maxillary  branch. 

Meatuses  (three). 

Superior,  above  superior  turbinated. 

Middle,  between  two  turbinated. 

Inferior,  below  inferior  turbinated. 

Blood  Supply. 

Superior  coronary,  external  nasal,  palato-labial  and  ophthalmic 
arteries. 

Taste. 

The  mucous  membrane  of  the  tongue  is  the  seat  of  this  sense. 
The  tongue  and  the  mucous  membrane  have  been  already  de- 
scribed.    (See  Mouth.) 

Nerve  Supply. 

Posterior  third  by  ninth  nerve   (glosso-pharyngeal). 

Anterior  two-thirds  by  chorda  tympani  (from  seventh). 

The  nerves  end  in  the  taste  (or  gustative)  bulbs,  which  are 
found  about  the  calcijorm  and  fungiform  papillae.  They  are  fusi- 
form in  shape,  the  upper  extremity  reaching  the  mucous  mem- 
brane. The  nerve  is  found  in  the  centre,  and  on  the  sides  are 
protective  cells,  fusiform  in  shape,  each  with  a  special  nucleus. 

Auditory  Apparatus. 

Divided  into  three  parts,  the  external,  middle  and  internal  ears, 
which  collect,  transmit  and  take  cognizance  of  sound.  The 
internal  ear,  the  essential  part  of  the  apparatus,  being  enclosed  in 
the  petrous  portion  of  the  temporal  bone. 

EXTERNAL    EAR. 

This  consists  of  the  external  auditory  canal  and  the  concha  or 
widened  appendage.  # 

The  Concha. 

This  is  pyramidal  in  shape,  its  apex  directed  forward  and 
upward,  convex  externally,  concave  internally.  It  consists  of  three 
cartilages,  ten  muscles,  a  fatty  cushion  and  integument. 

Cartilages. 

(i)  Conchal. — Of  the  general  shape  of  the  whole  concha,  and 
attached  by  the  (2)  Annular  cartilage  to  the  beginning  of  the 
external  auditory  meatus. 


158  EQUINE  ANATOMY. 

(3)  Scutijorm. — A  small  plate  lying  in  front  of  the  base  of  the 
concha  and  attached  to  it. 

Muscles. 

There  are  a  few  intrinsic  muscular  fibres  of  little  importance. 
Extrinsic  are — 

1.  Zygomatico-auricularis. 

Origin. — Zygomatic  process  of  temporal. 
Insertion. — Outer  side  of  base  of  concha. 
Action. — Carries   ear   forward. 

2.  Temporo-auricularis  externus. 
Origin. — Parietal  ridge. 

Insertion. — Conchal  and  scutiform  cartilages. 
Action. — Draws  ear  forward  and  inward. 

3.  Scuto-auricularis   externus. 
Origin. — Scutiform  cartilage. 
Insertion. — Inner  side  of  concha. 
Action. — Rotates  concha. 

4.  Cervico-auricularis  superior. 

Origin. — From  external  temporo-auricular. 
Insertion. — Posterior  face  of  concha. 
Action. — Draws  it  back. 

5.  Cervico-auricularis  tnedius. 
Origin. — Preceding  and  following. 
Insertion. — Base  of  concha. 

Action. — Rotates  concha  out  and  back. 

6.  Deep  cervico-auricularis. 

Origin. — Under  and  upper  extremity  of  parotid. 
Insertion. — Base  of  concha. 
Action. — Like  preceding. 

7.  Parotido-auricularis. 

Origin. — Outer  surface  of  parotid. 
Insertion. — Base  of  and  outside  of  concha. 
Action. — Adducts  ear. 

8.  Temporo-auricularis  internus. 

Origin. — Under  superficial  of  same  name,  from  intra-parietal 
ridge. 

Insertion. — Inner  side  of  concha. 
A  ction. — Adductor. 


VISCERAL   ANATOMY.  1 59 

9.  Scuto-auricularis  internus. 
Origin. — Beneath  scutiform. 
Insertion. — Base  of  concha. 

Action. — Antagonizes  No.  3.  Turns  ear  outward  and  back- 
ward. 

10.  Mastoido-auricularis. 

Origin. — Margin  of  auditory  meatus. 
Insertion. — Into  base  of  concha. 
^Action. — Constricts  meatus. 
Skin. — Thin,  vascular,  and  covered  with  fine  hairs. 

EXTERNAL  AUDITORY  CANAL. 

This  is  a  short  canal  lodged  in  the  petrous  portion  of  the  tem- 
poral bone,  commencing  at  the  external  meatus  and  ending  at  the 
middle  ear,  being  shut  off  from  that  cavity  by  the  membrana 
tympani.  The  canal  is  lined  with  thin  skin  which  contains  a 
number  of  ceruminous  glands  which  secrete  cerumen  or  wax. 

MIDDLE   EAR   OR  TYMPANUM. 

The  tympanum  is  a  cavity  situated  in  the  interior  of  the  tem- 
poral bone  at  the  junction  of  its  mastoid  and  petrous  portions, 
communicating  with  the  pharynx  by  a  canal  lined  with  mucous 
membrane,  the  Eustachian  tube.  It  has  an  external  wall  formed 
by  the  membrana  tympani,  an  internal,  shutting  it  off  from  the 
internal  ear,  showing  two  openings,  the  fenestra  ovalis  and  fenestra 
rotunda,  separated  by  an  elevation,  the  promontory,  and  a  circum- 
ference, which  shows  the  openings  of  many  mastoid  cells.  It  is 
lined  with  mucous  membrane  continuous  with  that  of  the  pharynx, 
and  covered  with  pavement  epithelium. 

The  Membrana  Tympani  shuts  off  the  external  meatus  from 
the  tympanum,  is  concave  externally,  convex  internally,  set 
strongly  in  a  bony  depression  and  adherent  internally  to  the 
handle  of  the  malleus.  It  consists  of  three  layers,  a  middle  fibrous 
and  muscular,  an  external  of  skin,  and  an  internal  of  mucous 
membrane. 

The  Fenestra  Ovalis,  lying  in  front  of  the  promontory,  is  oval 
in  shape,  closed  by  the  base  of  the  stapes,  and  communicates  with 
the  vestibule. 

The  Fenestra  Rotunda  communicates  with  the  scala  tympani 
and  is  closed  in  by  a  membrane. 


160  EQUINE   ANATOMY. 

The  Mastoid  Cells  are  small  cavities  communicating  with  the 
tympanum  and  lined  by  a  reduplication  of  its  mucous  membrane. 

The  Ossicles  of  the  tympanum  are  four  in  number,  the  malleus, 
incus,  os  orbicular e  and  stapes. 

The  malleus  (hammer)  shows  a  head  for  articulation  for  the 
incus,  a  handle  for  articulation  with  the  membrane,  and  a  neck 
showing  two  processes  of  insertion  {processes  gracilis  and  brevis). 

The  incus  (anvil)  shows  a  body  and  two  processes,  the  superior 
ending  in  a  blunt  point,  the  inferior  being  attached  to  the  orbicular 
bone. 

The  os  orbiculare,  a  small,  disk-shaped  bone,  lies  between  the 
incus  and  stapes. 

The  stapes  (stirrup)  is  shaped  like  a  stirrup  and  has  a  head 
articulating  with  the  preceding,  two  branches,  united  at  a  base, 
which  fills  in  the  fenestra  ovalis.  They  are  held  together  by 
unimportant  ligaments. 

Muscles. — (Two  of  importance  only.) 

Tensor  tympani. 

Origin. — From  Eustachian  tube. 

Insertion. — Into  neck  of  malleus. 

Action. — Carries  handle  of  malleus  inward,  thus  making  mem- 
brana  tympani  tense. 

Stapedius. 

Origin. — Wall  of  tympanum,  near  f.  vestibuli. 

Insertion. — Head  of  stapes. 

Action. — Tensor  of  membrana. 

The  Eustachian  tube  is  a  canal  of  cartilaginous  material  running 
from  the  tympanum  downward  for  a  distance  of  four  inches,  to 
near  the  guttural  openings  of  nasal  cavity,  where  it  is  expanded 
into  the  guttural  pouches.     It  is  covered  by  the  stylo-pharyngeus. 

Function. — Maintains  the  equilibrium  of  air  inside  the  mem- 
brana tympani. 

The  guttural  pouches  are  two  elongated  cavities  communicating 
with  the  pharynx,  and  lying  on  its  sides. 

They  are  in  relation  externally  to  the  carotid  and  parotid  glands, 
and  have  a  capacity  of  three-fourths  of  a  pint,  though  capable  of 
much  greater  distention. 

The  mucous  membrane  is  thick,  strong  and  well  lubricated  with 
mucus. 

Function. — Probably  connected  with  hearing  in  some  way,  and 
also  with  phonation. 


VISCERAL   ANATOMY.  161 


THE   INTERNAL  EAR. 


The  structures  of  the  internal  ear  are  contained  in  the  petrous 
portion  of  the  temporal  bone  forming  the  bony  labyrinth,  the 
parts  themselves  being  called  the  membranous  labyrinth. 

The  Bony  Labyrinth  consists  of  the  vestibule,  semicircular 
canals  and  cochlea. 

The  vestibule  lies  inside  the  inner  wall  of  the  tympanum, 
receiving  the  fenestra  ovalis,  the  five  openings  of  the  semicircular 
canals  above,  the  commencement  of  the  scala  cochlea  and  the 
openings  for  the  vestibular  branches  of  the  eighth  nerve. 

The  semicircular  canals  are  three  in  number,  opening  at  five 
points.     They  are  named  the  superior,  posterior,  and  external. 

The  Cochlea  (or  snail  shell)  is  situated  outside  and  below 
the  vestibule,  consisting  of  a  central  stem,  the  modiolus,  with  a 
twisted  partition,  the  lamina  spiralis,  running  about  it,  and  divid- 
ing the  cochlea  into  two  portions,  that  above  the  partition,  the 
scala  tympani,  communicating  with  the  tympanum  by  the  fenes- 
trum  'rotundum;  that  below,  the  scala  vestibuli,  entering  the 
vestibule.  The  lamina  does  not  quite  reach  the  outer  wall  of 
the  cochlea. 

The  Membranous  Labyrinth  consists  also  of  the  vestibule, 
semicircular  canals  and  cochlea. 

The  vestibule  consists  of  two  thin  sacs,  a  superior  or  utricle, 
communicating  with  .the  semicircular  canals,  and  inferior  or 
saccule,  in  contact  with  the  former. 

The  structure  of  the  vestibule  is  an  external  fibrous  coat  and 
internal  epithelial  lining,  with  some  calcareous  particles  (the 
otoliths)  at  the  entrance  of  the  nerves. 

The  Membranous  Semicircular  Canals  fill  the  bony  canals, 
and  are  of  the  same  structure  as  the  vestibule. 

One  of  their  extremities  is  dilated,  the  ampulla. 

The  Membranous  Cochlea. 

The  lamina  spiralis  is  continued  by  two  membranes  to  the  per- 
iphery of  the  cochlea,  dividing  it  into  the  two  already  described — 
the  s.  tympani  below  and  s.  vestibuli  above — and  a  median  one 
between  the  two,  the  auditive,  which  contains  the  organ  of  Corti, 
a  large  number  of  small  epithelial  elements,  resting  on  the  mem- 
brana  basilaris,  and  having  above  the  membrane  of  Corti. 


162  EQUINE   ANATOMY. 

The  organ  of  Corti  is  very  intimately  connected  with  the 
perception  of  sound.  The  scala  vestibuli  is  again  divided  by  the 
membrane  of  Reissner  into  two  more  canals. 

The  Fluids  of  the  internal  ear  are  the  endolymph,  limpid  and 
watery,  inside  the  membranous  labyrinth,  and  the  perilymph 
outside  the  membranous  portion. 

The  Nerve  Supply  is  from  the  eighth  or  auditory  nerve,  which 
splits  up  into  vestibular  branches,  to  the  utricle,  saccule  and  ampulla 
and  cochlear  branches  to  the  different  scalae  of  the  cochlea. 


SIGHT. 

The  eyes  are  two  globular  bodies,  situated  in  the  orbital  cavi- 
ties, that  collect  impressions  of  light,  these  impressions  being 
carried  to  the  brain  by  the  optic  or  second  pair  of  nerves. 

THE   ORBITS. 

Two  bony  cavities,  situated  at  the  upper  and  anterior  part  of 
the  face,  containing  the  organs  of  vision.  The  bones  entering 
into  their  formation  are  at  its  base  the  zygoma,  the  zygomatic 
process  of  the  temporal,  malar,  frontal  and  lachrymal. 

On  the  inner  side  are  found  the  sphenoid,  palate  and  superior 
maxilla.  The  orbit  is  continuous  behind,  with  the  temporal 
fossa.     On  its  inner  side,  anteriorly,  is  seen  the  lachrymal  fossa. 

The  foramina  opening  into  it  are  the  palatine,  spheno-palatine, 
superior  dental,  optic,  pathetic,  lacerated  and  rotundum. 

THE   EYE. 

The  organs  of  vision  consist  of  the  two  eyeballs  and  appendages. 

The  eyeball  is  spheroidal  in  shape,  a  little  longer  in  its  antero- 
posterior diameter,  where  it  is  continued  by  the  cornea.  It  lies 
in  the  fat  of  the  orbit,  held  in  position  by  its  muscles,  and  con- 
sists of  three  tunics  surrounding  the  humors. 

TUNICS. 

The  tunics  of  the  eye  are  the  (i)  sclerotic  and  cornea,  (2)  choroid 
and  iris,  and  (3)  retina. 

The  Sclerotic  is  the  white,  dense,  outer  coat  into  which  the 
muscles  are  inserted.     The  choroid  lies  in  contact  with  it  inter- 


VISCERAL  ANATOMY.  163 

nally.  It  is  continued  in  front  as  the  cornea,  and  is  pierced 
behind  for  the  optic  and  ciliary  nerves  and  central  artery. 

The  Cornea  is  the  anterior  one-sixth  of  the  sclera.  It  is 
shaped  like  a  watch-glass,  convex  in  front,  and  transparent.  It 
is  composed  of  a  middle  proper  structure  of  connective  tissue,  an 
anterior  layer  from  the  conjunctiva,  and  a  posterior,  elastic  in 
structure,  the  membrane  of  Descemet. 

The  Choroid  lies  between  the  sclera  and  retina,  and  is  a  thin, 
brownish,  vascular  membrane. 

Its  coats  from  without  inward  (Strangeways)  are — 

1.  Membrana  jusca,  of  connective  tissue,  vessels  and  nerves. 

2.  Vascular  layer,  containing  many  veins,  the  venae  vorticosae. 

3.  Tunica  Ruyschiana,  of  capillary  vessels  from  ciliary  arteries. 
(The  pigment  layer  of  the  retina  was  formerly  included  as  a 

layer  of  the  choroid.) 

The  Ciliary  Muscle  is  a  band  of  circular  unstriped  fibres 
running  from  the  junction  of  the  cornea  and  sclera  to  the  iris. 
Its  function  is  connected  with  accommodation. 

The  Ciliary  Processes  are  folds  of  the  choroid  anteriorly, 
about  sixty  to  eighty  in  number  and  y1^  inch  in  length. 

The  Iris  is  a  circular  curtain,  a  continuation  of  the  choroid 
anteriorly,  yellowish-brown  in  color,  with  a  central  opening,  the 
pupil. 
•  Structure. 

(1)  Anterior  epithelial  layer,  continuous  with  the  posterior  cor- 
neal layer;  (2)  middle  muscular,  of  circular  and  radiated  untriped 
muscular  fibres,  supplied  by  the  ciliary  ganglion;  (3)  posterior 
epithelial  or  uvea,   with  numerous  pigment  cells. 

The  Retina,  or  internal  tunic,  is  the  expansion  of  the  optic 
nerve  ending  in  a  number  of  folds  anteriorly,  the  zone  of  Zinn. 
Its  layers  from  without  inward  are — 

1.  Pigmentary,  of  hexagonal,  pigment  cells,  formerly  ascribed 
to  choroid. 

2.  Layer  of  rods  and  cones. 

3.  External  granular  layer. 

4.  Intermediate  layer. 

5.  Inner  granular  layer. 

6.  Molecular  layer. 

7.  Ganglionic  layer. 

8.  Optic  nerve  fibres. 


164 


EQUINE   ANATOMY. 


At  the  point  of  entrance  of  the  optic  nerve,  there  is  an  oval 
point  \  inch  in  diameter,  where  all  nerve  elements  are  absent; 
this  is  the  blind  spot. 


Fig.  26. 


THEORETICAL    SECTION    OF  THE    HORSE  S    EYE. 

Optic  nerve;  b,  Sclerotic;  c,  Choroid;  d,  Retina;  e,  Cornea;  /,  Iris;  g,  h,  Ciliary 
circle  (or  ligament)  and  processes  given  off  by  the  choroid,  though  represented 
as  isolated  from  it,  in  order  to  indicate  their  limits  more  clearly;  i,  Insertion  of 
the  ciliary  processes  on  the  crystalline  lens;  /",  Crystalline  lens;  k,  Crystalline 
capsule;  /,  Vitreous  body;  m,  n,  Anterior  and  posterior  chambers;  o,  Theoretical 
indication  of  the  membrane  of  the  aqueous  humor;  p,  p,  Tarsi;  g,  g,  Fibrous 
membrane  of  the  eyelids;  r,  Elevator  muscleof  the  upper  eyelid;  s,  s,  Orbicularis 
muscle  of  the  eyelids;  t,  t,  Skin  of  the  eyelids;  u, Conjunctiva  ;  v,  Epidermic  layer 
of  this  membrane  covering  the  cornea;  x.  Posterior  rectus  muscle;  y,  Superior 
rectus  muscle;  z.  Inferior  rectus  muscle;  w,  Fibrous  sheath  of  the  orbit  (or  or- 
bital membrane). 


Humors. 

These  are  the  aqueous  and  vitreous  'humors,  and  crystalline 
humors. 
The  Aqueous    humor  fills  up  the  space  lying  between  the 


VISCERAL  ANATOMY.  1 65 

cornea,  pupil  and  iris  (anterior  chamber),  is  alkaline  in  reaction, 
consisting  of  water  with  -£$  solids. 

The  Vitreous  fills  up  the  space  inside  the  retina  and  lens.  It 
consists  of  gelatinous  tissue. 

The  crystalline  lens  is  T5^  by  T%  inches,  lies  behind  the  pupil 
and  in  front  of  the  vitreous.  It  is  a  double  convex  lens  of  con- 
centric layers,  with  an  external  capsule. 

MUSCLES   OF   THE   EYELID. 

Orbicularis  palpebrarum. 
Origin. — Lachrymal  tubercle. 
Insertion. — Skin  of  both  eyelids. 
Action. — -Sphincter  of  lids. 
Levator  palpebral  superioris  externus. 

Origin. — External  surface  of  frontal  near  supra-orbital  fora- 
men. 
Insertion. — Into  orbicularis. 
Action. — Wrinkles  skin  of  upper  lid. 
Levator  palpebrce  superioris  internus. 
Origin. — Superior 'border  of  optic  foramen. 
Insertion. — Inner  surface  of  upper  lid  and  tarsal  cartilage. 
Action. — Raises  upper  lid. 
Nerve  Supply. 
The  latter  by  motor  oculi,  the  others  by  facial. 

MUSCLES   OF   GLOBE. 

Retractor  oculi. 

Origin. — Optic  foramen. 

Insertion. — Outer  and  back  part  of  sclera. 

Superior,  inferior,  external  and  internal  recti. 

Origin. — Margin  of  optic  foramen. 

Insertion. — Above,  below,  outside  and  inside  sclera. 

Superior  oblique. 

Origin. — Optic  foramen,  passes  to  internal  wall  of  orbit  through 
a  cartilaginous  loop. 

Insertion. — Into  sclera,  between  superior  and  external  recti. 

Inferior  oblique. 

Origin. — Lachrymal  fossa. 

Insertion. — Under  sclera. 

Action. — The  superior  rectus  turns  the  globe  upward,  the 
inferior  down,  the  external  out,  the  internal  in,  the  superior  oblique 


1 66  EQUINE   ANATOMY. 

upward  and  outward,  the  inferior  oblique  downward  and  inward, 
and  the  retractor  oculi,  as  its  name  implies. 

Nerves. — The  sixth  nerve  supplies  the  external  rectus  and 
retractor  oculi,  the  fourth  the  superior  oblique,  and  the  third  the 
remainder. 

APPENDAGES   OF  THE   EYE. 

The  Eyebrows  are  small  and  furnished  with  long  hairs. 

The  Eyelids  are  two  in  number,  superior  and  inferior.  The 
angles  of  continuation  are  called  the  external  and  internal  canthi. 
They  are  covered  with  skin  externally  and  conjunctiva  internally, 
with  long  hairs  and  orifices  of  Meibomian  glands  on  the  edges. 
Their  framework  is  made  up  of  muscles  and  tarsal  cartilages,  two 
thin  plates,  the  upper  being,  the  larger. 

The  Meibomian  Glands  pour  out  a  sebaceous  matter  to 
lubricate  the  lids.  They  lie  between  the  cartilage  and  conjunc- 
tiva and  are  tubular  in  character. 

The  Conjunctiva  is  a  mucous  membrane,  thin  and  vascular, 
lining  the  lids  and  covering  the  anterior  part  of  the  globe. 

The  Membrana  Nictitans  is  an  accessory  lid  lying  at  the 
nasal  angle  of  the  orbit,  composed  of  elastic  cartilage.  It  serves 
to  remove  foreign  bodies  from  the  eye. 

The  Caruncle  is  a  small,  red  elevation  at  the  inner  canthus, 
which  directs  the  tears  toward  the  puncta. 

The  Tear  Apparatus  consists  of  the  lachrymal  gland,  canalic- 
uli,  lachrymal  sac  and  nasal  duct. 

The  lachrymal  gland  is  conglomerate,  lying  under  the  roof  of 
the  orbit,  and  secretes  the  tears,  which  empty  on  the  inner  sur- 
face of  the  upper  lid. 

The  excess  of  tears  enter  the  canaliculi,  two  small  canals  in  the 
upper  and  inner  lids,  which  run  from  openings  on  the  lids,  the 
puncta  to  the  lachrymal  sac,  a  dilatation  in  the  lachrymal  fossa. 
This  sac  forms  the  beginning  of  the  nasal  duct,  which  runs  down 
in  the  lachrymal  bone  as  a  membranous  canal,  to  end  near  the 
nostril  on  its  inner  side. 

The  Ocular  Sheath  is  a  firm,  fibrous  membrane  binding  the 
structures  of  the  orbit  together. 

Blood  Supply. 

Ophthalmic  from  internal  maxillary,  giving  off  ciliary,  arteria 
centralis  retinoz,  supra-orbital,  and  lachrymal  to  the  gland. 


VISCERAL   ANATOMY.  167 


THE  SENSE  OF  TOUCH. 

The  special  sense  of  touch  is  located  in  the  skin,  being  more 
marked  in  the  lips  and  extremities. 

THE  SKIN. 

The  skin  is  the  outer,  enveloping  membrane  of  the  body,  and 
continuous  with  the  outer  limits  of  the  internal  mucous  mem- 
branes. It  is  divided  into  the  derma  or  cutis  vera,  internally,  and 
the  epidermis,  externally. 

The  Derma  forms  the  greater  part  of  the  thickness  of  the  skin, 
being  continuous  with  the  subcutaneous  connective  tissue,  intern- 
ally, and  the  epidermis,  externally,  where  it  contains  little  eleva- 
tions, the  papilla.  It  is  composed  internally  of  loose  meshed 
tissue,  the  corium,  and  externally  of  the  papilla,  arranged  in 
parallel  rows  about  T^-$  of  an  inch  in  length. 

The  Epidermis,  or  cuticle,  lying  upon  the  derma,  is  more  or 
less  pigmented,  and  consists  of  an  internal  deep  layer  or  rete 
mucosum,  containing  soft  pigment  cells  and  a  superficial  or  horny 
layer  of  condensed,  horny,  flattened  cells. 

The  Appendages  of  the  Skin  are  the  hairs,  sudoriferous  and 
sebaceous  glands  and  horny  parts. 

The  Hairs. 

The  hairs  are  modifications  of  skin,  and  are  divided  into  the 
hair  proper,  forming  the  coat,  and  horse  hair,  long  and  flowing, 
found  in  the  forelock,  mane,  tail,  eyelashes,  lips  and  fetlock. 

Structure. 

Hairs  consist  of  a  free,  projecting  portion,  the  shaft,  of  three 
layers,  an  external  of  flattened  epidermal  scales,  a  middle  or  cor- 
tical of  narrow,  epithelial  lamellae,  pigment  and  air  globules, 
and  an  internal  or  medullary  of  rectangular  cells  with  fat  and  air 
globules;  a  root  lying  imbedded  in  the  skin,  in  an  involution,  the 
hair  follicle  with  external  and  internal  sheaths  and  resting  on  the 
papilla,  from  which  it  takes  its  nutrition  and  growth. 

The  Sudoriferous  Glands  are  attached  to  the  skin,  consisting 
of  a  curled  tubule  lying  in  the  corium  and  a  spiral  duct  passing 
up  through  the  derma  and  epidermis,  lined  with  epithelium. 
Their  function  is  the  regulation  of  animal  heat,  and  also  are  con- 
nected with  excretion. 


1 68  EQUINE   ANATOMY. 

The  Sebaceous  Glands  empty  into  the  hair  follicles  or  on  the 
skin  independently.  They  consist  of  vesicles  filled  with  fatty  and 
epithelial  tissue,  opening  into  a  common  duct.  Their  junction  is 
lubrication  and  protection,  as  well  as  preservation  of  the  elasticity 
of  the  hair. 

The  Horny  Parts. 

These  comprise  the  chestnuts,  ergot  and  hoofs. 

The  Chestnut  is  a  small  growth  of  epithelial  tissue,  oval  in 
form,  at  the  inner  side  of  the  upper  metatarsal  region,  where  it  is 
smaller,  and  at  the  inner  side  of  the  forearm. 

The  Ergot  is  a  similar  structure  attached  to  the  skin  of  the  fet- 
lock. 

The  Hoof. — The  hoof  is  the  complicated  apparatus  surround- 
ing the  third  or  distal  phalanx,  navicular  bone,  and  part  of  the 
second  phalanx.  The  bones,  articulations,  muscles,  nerves  and 
vessels  may  all  be  found  under  their  headings.  It  also  consists 
of  the  complementary  apparatus,  keratogenous  membrane  and 
hoof  proper. 

THE   COMPLEMENTARY   APPARATUS. 

This  consists  of  the  fibro-cartilages,  two  in  number,  united  be- 
hind and  below  by  the  plantar  cushion. 

The  Cartilages  are  two  in  number,  attached  in  front  to  the 
anterior  lateral  ligament,  behind  to  the  basilar  and  retrossal  proc- 
esses and  plantar  cushion;  they  are  thin  above,  with  a  notch  be- 
hind for  vessels,  thick  below,  concave  internally,  with  vascular 
foramina,  and  convex  externally,  also  with  foramina  for  vessels. 

They  are  composed  of  fibrous  and  cartilaginous  tissue. 

The  Plantar  Cushion  is  wedge-shaped,  lying  between  the  car- 
tilages and  below  the  insertion  of  the  perforans. 

The  superior  surface  lies  on  the  expansion  of  the  perforans,  and 
is  attached  by  bands  to  the  ergot,  metacarpus  and  os  pedis.  The 
inferior  surface  is  covered  by  the  keratogenous  membrane,  and 
shows  the  pyramidal  body  moulded  on  the  frog  with  its  apex  for- 
ward and  two  diverging  arms  behind.  Its  base  terminates  in  two 
bulbs. 

The  summit  is  attached  to  the  plantar  surface  of  the  os  pedis. 

The  lateral  borders  are  attached  to  the  cartilages. 

Its  structure  is  of  fibrous,  elastic  and  adipose  tissue,  with  ves- 
sels and  nerves. 


VISCERAL  ANATOMY. 


169 


The  Keratogenous  Membrane  encloses  the  whole  of  the  pre- 
ceding structures,  being  itself  enclosed  by  the  hoof. 

It  consists  of  the  coronary  cushion,  velvety  and  laminal  tissues. 


Fig.  27. 


LONGITUDINAL    MEDIAN    SECTION    OF  THE    FOOT. 

i.  Anterior  extensor  of  the  phalanges,  or  extensor  pedis;  2,  Lateral  extensor,  or  ex- 
tensor suffraginis;  3.  Capsule  of  metacarpophalangeal  articulation;  4,  Large 
metacarpal  bone;  5,  Superior  flexor  of  the  phalanges,  or  perforatus;  6,  Deep 
flexor,  or  perforans;  7,  Sheath;  8,  Bursa;  9,  Sesamoid  bone;  10,  Ergot  and  fatty 
cushion  of  fetlock;  11,  Crucial  ligament;  12,  Short  sesamoid  ligament;  13,  First 
phalanx;  14,  Bursa;  15,  Second  phalanx;  16,  Navicular  bone;  17,  Plantar  cushion; 
18,  Third  phalanx;  19,  Plantar  surface  of  hoof;  20,  Sensitive  or  keratogenous 
membrane  of  third  phalanx. 


The  Coronary  Cushion  resembles  the  derma,  and  forms  the 
upper  border  of  the  membrane.  Its  inferior  boundary  is  a  white 
ring.  Its  superior  has  a  margin,  the  perioplic  ring.  The  extrem- 
ities end  behind  in  the  velvety  tissue.  On  its  surface  are  numer- 
ous papillae. 

The  Velvety  Tissue  is  also  papillary  in  structure,  covering  the 
plantar  surface  of  the  third  phalanx  and  plantar  cushion.  At 
12 


170  EQUINE   ANATOMY. 

its  centre  it  is  in  relation  with  the  pyramidal  body  and  frogs,  ex- 
ternally with  the  horny  sole. 

The  Laminal  (or  Podophyllous)  Tissue  consists  of  500  or 
600  leaves  on  the  front  and  sides  of  the  os  pedis,  ending  below  in 
the  plantar  cushion,  each  one  having  five  or  six  villi  lodged  in  de- 
pressions in  the  sole.  The  laminae  have  secondary  folds  attached 
to  them  at  their  sides.  They  are  composed  of  papillary  structure, 
like  the  remainder  of  the  membrane,  and  are  the  principal  seat 
of  the  tactile  sense. 

Fig.  28. 


PLANTAR   OR   GROUND    SURFACE   OF  A    HOOF;    RIGHT    FOOT. 

The  interval  from  a  to  a  represents  the  toe.     From  a  to  b,  b,  outside  and  inside 

quarters;  c,  o.   Commencement  of  bars;  d,  d,  Inflexions  of  wall  at  the  heels,  or 

buttresses;  "  e,  Lateral  lacuna;  /,  /,  /,  Sole;  g,  White  line;  g1 ,  g'.  Ditto  between 

the   sole  and  bar;  h,  Body  of  frog;  i.  Branch  of  frog;  k,  k,  Glomes,  or  heels  of 

frog;  /,  Median  lacuna. 

The  Hoof. 

The  box  that  envelops  the  foot  is  divided  into  three  parts,  the 
wall,  sole  and  frog. 

The  wall,  or  crust,  covers  the  front  of  the  foot,  and  terminates 
behind  by  turning  into  the  plantar  cushion.  Its  front  is  called 
the  toe,  the  sides  of  the  toe  being  either  the  inner  or  outer  toe,  its 
lateral  regions  the  quarters,  the  angle  behind,  where  it  turns  into 
the  plantar  cushion,  the  heels,  and  these  terminations  the  bars. 

The  external  surface  is  smooth  and  convex,  covered  by  a  thin, 
horny  layer,  the  periople. 

The  internal  surface  is  continuous  with  the  laminal  tissue. 


VISCERAL   ANATOMY.  171 

The  superior  border  shows  depressions  for  the  villosities  of  the 
coronary  tissue. 

The  inferior  border  is  continuous  with  the  sole,  and  behind  is 
carried  inward  as  the  bars. 

The  Sole  is  a  thick,  horny  plate,  forming  the  inferior  face  of 
the  hoof.  Its  inferior  face  is  concave,  and  its  superior  has  aper- 
tures for  the  villi  above  it.  Its  outer  border  is  continuous  with 
the  external  surface  of  the  wall,  its  inner,  as  the  bars,  lie  outside 
the  frog. 

The  Frog  is  V-shaped,  its  base  behind,  apex  in  front,  separated 
by  a  median  depression.  On  either  side  are  lateral  depressions; 
at  its  base  are  two  lateral  elevations;  the  glomes.  It  lies  between 
the  bars  and  below  the  plantar  cushion. 

Structure  of  Hoof. — Horny  tissue,  a  modification  of  the  epi- 
dermis. 


EQUINE  PHYSIOLOGY. 


Physiology  is  the  study  of  the  functions  or  actions  of  living 
structures  or  organs. 
Equine  Physiology  treats  of  its  application  to  the  horse. 

THE  CIRCULATION. 

The  circulatory  system  consists  of  a  central  organ,  the  heart, 
arteries,  veins,  and  lymphatics  (for  anatomical  structure  see 
above),  the  blood  and  lymph. 

THE  BLOOD. 

The  blood,  the  great  nutritive  fluid  of  the  body,  is  about  T^  of 
the  bodily  weight  in  amount. 

Its  composition  in  ioo  parts  venous  blood — 

Corpuscles,  32.62 

Plasma, 67.38 

100.00 

The  corpuscles  consist  of — 

Water, 56 

Solids, 43 

99 
The  plasma  consists  of — 

Solids,  9.16 

Water,  90.84 

100.00 

(173) 


174  EQUINE   PHYSIOLOGY. 

The  solids  of  plasma  are — 

Fibrin, 1.91 

Albumin, 7.76 

Fats, 12 

Extractives, 40 

Soluble  salts, 64 

Insoluble  salts, 17 

10.10 

The  Specific  Gravity  of  the  horse's  blood  is  1055,  its  Reaction 
alkaline,  and  its   Temperature  36.5   to  37.8   Cent.     (Charles.) 

The  corpuscles  are  found  in  two  forms,  the  red  and  white. 

The  red  corpuscles  are  bi-concave  disks,  with  no  nuclei,  tending 
to  adhere  in  rolls,  with  a  diameter  of  .005  mm.  They  contain 
the  coloring  matter,  the  haemoglobin,  which  in  the  horse  contains 
43  per  cent,  of  iron,  and  also  C,  H,  N,  O,  and  S  (Preyer).  The 
haemoglobin  forms  about  90  per  cent,  of  the  red  disks  (Smith). 
Their  function  is  to  absorb  and  carry  oxygen. 

The  white  corpuscles  are  much  less  numerous  than  the  red,  the 
proportion  being  on  an  average  one  white  to  300  red.  They  are 
globular  in  shape  and  are  0.0 1  mm.  in  diameter,  and  contain  sev- 
eral nuclei.  They  are  derived  from  lymphoid  tissue,  and  are 
probably  developed  into  red  corpuscles.  They  have  the  power 
of  amoeboid  movement  by  pushing  out  processes,  and  of  passing 
through  the  walls  of  vessels.    . 

COAGULATION   OF   BLOOD. 

When  blood  is  placed  in  a  vessel  after  removal  from  the  body, 
it  goes  through  a  process  called  coagulation:  First,  in  a  few  min- 
utes a  yellow  scum  appears  on  top,  the  buffy  coat;  second,  the  cor- 
puscles settle  to  the  bottom,  forming  a  reddish  layer.  Then  drops 
of  serum  are  seen  on  the  sides  and  top.  In  12  or  15  hours  the 
serum  and  clot  are  completely  separated. 

The  serum  differs  from  plasma  in  not  containing  fibrin. 

The  specific  gravity  of  plasma  is  1027-1028. 

Theory  of  Coagulation  (Schmidt). 

Fibrinogen  and  fibrinoplastin,  with  the  fibrin-ferment,  derived 
probably  from  white  corpuscles,  come  together  and  cause  co- 
agulation. 

Coagulation  is  hastened  by  a  temperature  of  ioo°  F.,  contact 


THE  CIRCULATION.  1 75 

with  air,  rough  surfaces  and  rest,  and  retarded  by  cold,  neutral 
salts  in  excess,  exclusion  of  air,  etc.     (Brubaker.) 

Arterial  Blood  contains  more  oxygen  and  less  carbon  dioxide 
than  venous;  is  scarlet  in  color,  from  the  presence  of  oxy-haemo- 
globin.     Venous  blood  is  purple  in  color. 

The  blood  of  the  portal  vein  is  rich  in  water,  albuminous  mat- 
ter and  sugar,  and  the  hepatic  is  rich  in  corpuscles  and  sugar. 

CIRCULATION   OF  THE   BLOOD. 

The  blood  may  be  traced  from  the  left  ventricle,  through  the 
aorta,  to  the  capillaries,  where  it  passes  into  the  veins,  being  re- 
turned to  the  right  auricle  by  the  anterior  and  posterior  cavas. 
From  there  it  passes  to  the  right  ventricle,  through  the  pulmonary 
artery,  to  the  lungs,  where  it  is  oxygenated.  It  is  then  returned 
to  the  left  auricle  by  the  pulmonary  veins,  and  from  there  to  the 
ventricle.  By  this  it  is  seen  that  the  heart  is  the  central  organ 
of  the  circulation,  and  propels  the  blood  by  alternate  contractions 
and  dilatations.  The  contraction  is  known  as  the  systole,  the  dila- 
tation as  the  diastole. 

The  phenomena  attending  the  systole  are  a  hardening,  shorten- 
ing, a  movement  of  the  apex  downward,  and  a  twisting  of  the 
heart  from  left  to  right. 

//  the  heart's  cycle  is  divided  into  ten-tenths,  during  the  first 
four-tenths  the  ventricles  contract  simultaneously  and  the  auricles 
are  passive;  in  the  second  four-tenths  the  auricles  dilate  and  the 
ventricles  are  passive;  in  the  last  two-tenths  the  auricles  contract 
and  the  ventricles  dilate. 

The  sounds  of  the  heart  are  known  as  the  first  and  second, 
with  an  interval  of  silence  after  the  latter.  The  first  sound  occu- 
pies four-tenths,  the  second  three-tenths,  the  interval  of  silence 
three-tenths. 

The  first  sound  is  longer,  louder,  lower  in  pitch  and  more  boom- 
ing than  the  second,  and  in  caused  by  (1)  the  closing  of  the  auriculo- 
ventricular  valves;  (2)  the  apex  striking  against  the  chest;  (3)  the 
contraction  of  the  muscular  fibres;  (4)  the  sound  of  the  blood 
passing  through  the  interior. 

The  second  sound  is  shorter,  higher  in  pitch,  and  clicking,  and 
is  caused  by  the  closure  of  the  mitral  and  tricuspid  valves. 

The  force  of  the  heart,  or  vis  a  tergo,  is  more  than  sufficient  to 
carry  the  blood  through  the  system. 


176  .  EQUINE   PHYSIOLOGY. 

The  number  of  pulsations  of  the  heart  per  minute  are  from 
36  to  40.  In  the  new  born  horse  they  are  120,  and  at  the  end  of 
the  first  year  from  48  to  56. 

Their  relation  to  the  respiratory  movements  are  on  an  average 
one  to  four  (the  number  of  respiratory  acts  being  ten  per  minute, 
usually). 

The  capacity  of  the  ventricles  is  each  about  20  ounces. 

The  entire  blood  in  the  body  would  pass  through  the  left  ventri- 
cle in  66  seconds  in  an  animal  of  1000  pounds  weight,  assuming 
the  amount  of  blood  to  be  55T5o  pounds  (y¥  of  the  bodily  weight), 
and  requiring  44.4  pulsations. 

Arterial  Pressure  is  the  force  exerted  by  the  blood  on  the  ves- 
sels, and  is  measured  by  a  tube  introduced  into  some  of  the  large 
vessels.  In  the  carotid  the  blood  pressure  equals  32  mm.  of 
mercury;  in  the  brachial  150  mm. 

The  Arteries  may  be  divided  into  three  sets  (Flint),  the  largest 
ending  at  the  carotid  and  iliacs,  with  elastic  walls;  the  medium 
from  these  to  ^2  °f  an  mcn  m  diameter;  the  smallest  from  y1^  of  an 
inch  to  the  capillaries.  The  median  are  elastic  and  contractile, 
the  smallest  only  contractile. 

The  velocity  of  the  arterial  current  varies  in  the  different  arte- 
ries; it  is  the  greatest  during  systole,  least  during  diastole.  In 
the  carotid  it  is  300  mm.  per  second;  in  the  maxillary  165  mm. 
per  second;  metatarsal  56  mm. 

The  Capillaries  form  the  communication  between  the  arterial 
and  venous  vessels,  and  the  current  of  blood  is  much  slower,  only 
tu  to  A  mm-  Per  second,  the  blood  pressure  being  only  35  mm. 
In  the  capillaries  the  oxygen  is  absorbed  by  the  tissues. 

The  velocity  of  the  venous  current  varies:  in  the  jugular  vein 
being  100  mm.,  and  in  the  vena  cava  no  mm.  per  second.  The 
blood  pressure  of  the  venous  system  is  much  less  and  the  capacity 
much  more  than  the  arterial. 

Vierordt  showed  that  31.5  seconds  after  injection  of  a  salt  solu- 
tion into  one  jugular,  it  could  be  detected  in  the  vein  of  the  oppo- 
site side. 

The  valves  of  veins  prevent  damming  back  of  blood. 

The  flow  of  blood  is  kept  up  in  the  veins — 
1  st.  By  the  vis  a  tergo  of  the  heart. 
2d.  By  the  vis  a  fronte  or  suction  force  of  the  thorax. 
3d.  By  muscular  contraction  on  the  walls  of  the  veins. 


RESPIRATION.  1 77 

Action  of  the  nervous  system  on  circulation. 

The  heart  is  under  control  of  both  the  cerebro-spinal  and  sym- 
pathetic nervous  systems,  being  supplied  by  the  pneumogastric 
nerve  and  the  cervical  sympathetic,  there  being  also  probably 
some  intracardiac  sympathetic  ganglia. 

The  pneumogastric  has  an  inhibitory  action  on  the  heart,  as 
shown  by  section  of  the  nerves,  which  is  followed  by  an  increased 
frequency  of  the  heart's  action. 

The  sympathetic  has  an  accelerative  action  on  the  heart,  as 
shown  by  the  previous  experiment,  and  also  by  stimulation  of  the 
fibres,  which  is  followed  by  an  increased  number  of  pulsations. 
Stimulation  of  the  tenth  nerve  is  followed  by  decreased  pulsations, 
and  if  a  strong  current  is  used,  by  paralysis  of  the  heart  in  dias- 
tole, by  stimulation  of  its  inhibitory  action. 

Local  circulation  is  regulated  by  the  vaso-motor  nerves  of  the 
sympathetic  system.  They  are  known  as  vaso-dilators  and  vaso- 
contr  actors. 

RESPIRATION. 

Respiration  consists  of  an  appropriation  of  oxygen  by  the  tissues 
and  a  giving  off  of  carbonic  oxide  gas. 

The  respiratory  organs  consist,  from  above  downward,  of  the 
(1)  nasal  fossa,  (2)  pharynx,  (3)  larynx,  (4)  trachea,  (5)  bronchi, 
and  (6)  lungs.     (For  anatomical  descriptions,  see  Viscera.) 

The  different  steps  of  respiration  consist — 

1  st.  Of  the  introduction  of  atmospheric  air  into  the  lungs  in  in- 
spiration. 

2d.  Of  the  taking  up  of  oxygen  by  the  blood. 

3d.  Of  the  appropriation  of  oxygen  by  the  tissues. 

4th.  Of  the  exhalation  of  carbonic  acid  gas  in  expiration. 

In  Inspiration  the  air  passes  through  the  mouth  or  nasal  cavi- 
ties to  the  larynx,  the  glottis  being  dilated,  then  to  the  alveoli 
of  the  lungs,  which  it  distends. 

Muscles  of  Inspiration. 

The  diaphragm  is  the  most  important,  becoming  flattened, 
and  at  the  convexity  decreased. 

The  external  intercostals  and  supercostals  raise  the  ribs  and 
carry  them  forward,  thus  enlarging  the  lateral  diameter  of  the 
thorax. 


178  EQUINE   PHYSIOLOGY. 

In  forced  inspiration  we  have  coming  into  action  the  latissimus 
dorsi,  serratus  anticus  minor  and  scaleni. 

In  Expiration  the  air  is  forced  out  of  the  air  passages,  and  is 
in  a  passive  condition  usually,  except  in  forced  expiration. 

The  Muscles  of  Expiration  are  the  diaphragm,  coming  for- 
ward in  a  dome-shape,  decreasing  the  antero-posterior  diameter 
of  the  thorax. 

The  internal  intercostals,  triangularis  sterni  and  serratus  pos- 
ticus minor  act  by  carrying  the  ribs  backward. 

In  forced  expiration  we  have  coming  to  action  the  ilio-spinalis, 
external  and  internal  oblique,  transversalis  and  rectus  of  the  ab- 
dominal tunic,  by  depressing  and  retracting  the  posterior  ribs. 

Number  of  Respirations  per  Minute. 

Ordinary  movements, 10 

Walking  two  hundred  yards, 28 

Trotting  five  minutes, 52 

After  five  minutes'  gallop, 52 

(Colin-Smith.) 

Capacity  of  the  Lungs. 

In  man  the  extreme  breathing  capacity  of  the  lungs  is  over 
three  hundred  cubic  inches,  but  the  ordinary  capacity  is  only 
about  two  hundred  cubic  inches. 

The  tidal  air  is  that  breathed  in  and  out  in  tranquil  respiration. 

The  reserve  air  is  that  remaining  after  an  ordinary  expiration, 
but  which  can  be  expelled  in  a  full  expiration. 

The  residual  air  is  that  which  always  remains  after  a  forced 
expiration. 

The  complemental  air  is  that  which  can  be  taken  into  the  lung 
in  a  forced  inspiration. 

The  measurements  of  the  capacity  of  the  horse's  lungs  are  unim- 
portant, but  are  probably  about  five  or  six  times  as  extensive 
as  those  of  man. 

Changes  in  the  Air  in  its  Passage  through  the  Lungs. 

Atmospheric  air  consists  of — 

Nitrogen,  79.15  parts. 

Oxygen, 20.81     " 

Carbon  dioxide,  04     " 

100.00 


RESPIRATION.  1 79 

In  its  passage  through  the  lungs  it  loses  oxygen  and  gains  C02, 
expired  air  consisting  of — 

Nitrogen, 79-557 

Oxygen, 16.033 

C02 4-38 

99.970 

The  taking  up  of  oxygen  and  giving  off  of  C02  takes  place  by 
the  law  of  diffusion  of  gases,  illustrated  by  simple  experiments. 
That  expired  air  contains  C02  may  be  shown  by  blowing  into  a 
jar  of  lime-water,  the  liquid  becoming  turbid  from  the  change  into 
carbonate  of  lime,  and  giving  off  of  C02  in  form  of  bubbles.  These 
bubbles,  when  collected,  will  not  support  combustion,  and  turn 
blue  litmus  red. 

The  greater  part  of  the  oxygen  consumed  is  returned  in  the 
form  of  C02,  about  eight  out  of  ten  parts,  the  remainder  being 
thrown  off  by  the  urine  and  skin,  or  uniting  with  hydrogen  in  the 
body.  Solids  and  moisture  in  varying  proportions  are  also  thrown 
off. 
Changes  in  the  Blood  during  Respiration. 

Arterial  blood  contains  in  one  hundred  parts — 

Oxygen 20     volumes. 

Carbonic  dioxide 36 

Nitrogen 1-2 

Venous  blood  contains  in  one  hundred  parts — 

Oxygen 8-12  volumes. 

Carbonic  dioxide 46 

Nitrogen 1-2 

The  oxygen  exists  in  the  blood  in  the  red  blood  corpuscles  as 
oxy-hcemoglobin,  being  given  off  in  the  peripheral  capillaries,  and 
then  is  known  as  reduced  hcemoglobin. 

The  carbon  dioxide  exists  in  serum  in  a  loose  state  or  as  soluble 
carbonates. 

The  nitrogen  exists  in  solution  in  the  blood  serum,  and  can  be 
expressed  by  a  small  vacuum. 

The  gases  compose  about  60  per  cent,  of  the  volume  of  the 
blood. 

Nervous  Mechanism  of  Respiration. 

Respiration  is  involuntary  usually,  as  it  is  carried  on  during 


l8o  EQUINE   PHYSIOLOGY. 

sleep  and  in  unconsciousness  from  drugs,  though  it  is  also  modi- 
fied by  the  will. 

It  is  under  the  control  of  the  cerebro-spinal  nervous  system, 
though  the. sympathetic  forms  plexuses  at  the  root  of  the  lung. 

The  respiratory  centre  is  in  the  floor  of  the  fourth  ventricle 
and  a  puncture  at  that  point  stops  respiration  immediately.  If 
the  brain  is  removed  above  the  medulla,  the  act  still  goes  on.  If 
the  carotid  and  vertebral  arteries  are  ligated,  the  animal  develops 
dyspnoea  at  once,  owing  to  a  deficiency  of  oxygen  at  the  centre. 
The  nerves  of  respiration  are  the  two  phrenics,  two  pneumogas- 
trics,  intercostals  to  the  muscles  of  the  chest,  the  cervical  and 
lumbar  to  the  muscles  of  the  neck,  back  and  abdomen. 

The  Phrenics. — If  the  phrenics  are  both  cut,  the  diaphragm 
is  paralyzed;  if  a  single  one,  that  side  only  remains  passive.  If  a 
section  is  made  of  the  cord  above  the  fifth  cervical  nerve,  we 
have  instant  stopping  of  respiration,  due  to  paralysis  of  the  dia- 
phragm and  thoracic  muscles,  and  immediate  death.  Life  may 
be  continued  a  short  time  after  both  phrenics  have  been  divided, 
as  the  intercostal  muscles  still  act. 

The  Intercostals  act  very  simply  by  supplying  the  ordinary 
muscles  of  expiration  and  inspiration.  If  a  single  one  is  divided, 
the  remainder  do  its  work. 

The  Cervical  and  Lumbar  nerves  supply  the  muscles  gen- 
erally of  forced  inspiration  and  expiration. 

The  Pneumogastrics. — These  are  distributed  at  the  roots  of 
the  lungs,  and  if  one  is  cut,  respiration  becomes  very  slow.  Sec- 
tion of  both  causes  marked  decrease  in  respirations,  and  death  in 
four  or  five  days.  A  weak  galvanic  current  applied  to  the  nerve 
increases  the  number  and  force  of  the  respiratory  acts.  Stim- 
ulation of  the  central  end  of  its  divided  superior  laryngeal  branch 
causes  slow  respiration;  and  if  strong,  paralyzes  it  in  forced  ex- 
piration. 

ALIMENTATION. 

Alimentation  is  the  process  of  receiving  or  taking  nourishment; 
it  may  be  divided  into  digestion  and  absorption. 

Digestion  is  the  preparation  of  food  for  absorption. 

Absorption  is  the  process  by  which  the  digested  food  enters 
the  circulation. 

Nourishment  or  jood  is  necessary  to  repair  waste  and  for  the 
growth  of  the  animal. 


ALIMENTATION.  l8l 

The  jood  of  the  horse,  being  herbivorous,  consists  of  the  fol- 
lowing: 

(a)  Cereals,  as  wheat,  barley,  corn,  rice,  and  oats.  They  con- 
tain over  eighty  per  cent,  of  solids,  which  consist  of  albumin, 
small  amounts  of  fat,  carbohydrates,  and  non-nitrogenous  extract- 
ives. Corn  and  rye  are  rich  in  starch,  but  poor  in  albumin. 
Oats  are  very  rich  in  starch,  about  fifty  per  cent.,  and  also  con- 
tain nine  per  cent,  of  albumin  and  six  per  cent,  of  fat.  Oats  also 
contain  ferments,  which  digest  starch  and  proteids  as  well  as 
forming  lactic  acid;  assisting  the  stomach  very  materially  in 
digestion. 

(b)  Bulbs  and  roots,  as  potatoes,  containing  large  amounts  of 
water  and  starch;  fodder  and  sugar  beets;  cabbages,  containing 
a  large  amount  of  starch,  sugar  and  cellulose  in  small  amounts. 

(c)  Leguminous  plants,  as  peas  and  beans. 

(d)  Grasses,  as  prairie-hay,  rye-straw,  grass,  clover,  etc.  Green 
grass  contains  seventy-five  per  cent,  water,  clover  sixty  per  cent. 

(e)  Inorganic  matter  as  water,  common  salt,  lime  and  potassium 
salts,  and  iron. 

Sodium  chloride,  or  common  salt,  is  essential,  and  regulates 
endosmosis  and  exosmosis.  Other  salts  are  deposited  in  bone. 
The  iron  forms  the  coloring  matter  of  the  blood. 

The  Amount  of  Food  Required. 

The  horse  needs  daily  7500  grammes  of  hay  and  2270  of  oats, 
or  10  kilos  (22  lbs.)  of  hay,  and  2  kilos  (4.4  lbs.)  of  oats  to  every 
100  kilo  (220  lbs.)  of  body  weight.  Colin  says  that  the  horse 
will  eat  26  kinds  of  plants,  and  reject  212  (Meade-Smith). 

It  should  receive  daily  about  two  per  cent,  of  its  body  weight 
in  solid  food,  and  should  be  in  the  proportion  of  1  to  4  of  nitrog- 
enous and  non-nitrogenous  material.  The  different  steps  of 
digestion  are  prehension,  mastication,  salivary  digestion,  degluti- 
tion, gastric  and  intestinal  digestion,  absorption  and  defecation, 
or  expulsion  from  the  body  of  the  residue  not  required  for  ali- 
mentation. 

PREHENSION. 

Prehension  is  the  process  of  transferring  the  food  to  the  mouth, 
and  is  the  first  or  primary  act  of  digestion. 

The  upper  lip  carries  the  food  to  the  teeth,  the  long  neck  and 


182 


EQUINE    PHYSIOLOGY. 


head  being  carried  to  the  ground;  the  head  then  makes  a  quick 
movement  to  the  side,  and  the  food  is  carried  to  the  side  of  the 
mouth  to  be  ground  up  by  the  molars  (see  Teeth). 

Liquid  may  be  taken  in  by  (a)  sucking,  in  the  young;  (b)  pump- 
ing by  piston  action  of  tongue,  (c)  aspiration;  by  an  inspiratory 
movement.     The  second  one  is  the  most  often  used  by  the  horse. 

MASTICATION. 

Mastication  is  a  complex  act,  in  which  the  food  is  triturated  in 
the  mouth  between  the  two  jaws  and  teeth.  (For  anatomical 
considerations,  see  Teeth.) 

Movements   of  the  jaws. 

In  the  horse  these  are  depression,  elevation  and  rotation,  and 
in  mastication  make  eighty  strokes  per  minute.  The  incisors 
serve  to  bite  off  a  portion  of  food,  which  is  then,  by  the  tongue 
and  muscles  of  the  face,  carried  between  the  molars,  where  it  is 
comminuted  to  a  much  greater  degree. 


The  Time  of  the  Appearance  of  the  Teeth. 

Meade- Smith,  from  Kreutzer. 


ERUPTION. 

CHANGE. 

Incisors: — 

Central, .... 

Middle,.... 

Outer, 

Canines, 

Molars: — 

i, 

Before  or  few  days  after  birth. 
4  to  6  weeks. 
6  to  9  months. 
4  to  5  years. 

Before  or  few  days  after  birth. 
Before  or  few  days  after  birth. 
Before  or  few  days  after  birth, 
io  to  12  months. 
i|  to  2  years. 
4    to  5  years. 

2  years. 
3^  years. 
4^  years. 

2\  years. 
2\  years. 

3  years. 
3     years. 
3     years. 
3     years. 

2, 

2 

4, 

C, 

6, 

ALIMENTATION.  1 83 

SALIVARY  DIGESTION. 

For  anatomical  considerations,  see  Mouth. 

Saliva  is  alkaline  in  reaction,  its  specific  gravity  is  1004.5,  an(^ 
its  amount  in  24  hours  is  84  pounds.  Its  composition  (Meade- 
Smith,  from  Lassaigue)  is  as  follows  for  mixed  saliva — 

Water 992.00 

Mucus  and  albumin -. 2.00 

Carbonates 1.08 

Chlorides 4.92 

Phosphates,  etc traces. 

1000.00 

It  also  contains  epithelium,  mucin,  pytalin,  serum,  albumin, 
globulin  and  sulpho-cyanide  of  potassium. 

The  parotid  saliva  is  the  largest  in  amount  and  most  watery. 

The  sub-maxillary  is  viscid  and  contains  no  albumin,  and  the 
sub-lingual  is  very  viscid  and  contains  a  large  amount  of  solids. 

Action  of  the  Saliva. — It  has  a  mechanical  action,  by  lubricating 
the  bolus  of  food,  and  a  chemical  by  the  action  of  its  ferment, 
ptyalin.  This  converts  starch  into  sugar,  and  cane  sugar  into 
grape  sugar.  As  this  process  takes  several  minutes,  it  continues 
going  on  in  the  stomach. 

DEGLUTITION. 

'  The  act  of  deglutition  consists  of  the  passage  of  the  food  from 
the  mouth  to  the  stomach;  it  is  divided  into  three  stages;  the 
first  stage  comprises  the  passage  of  the  bolus  from  the  mouth 
through  the  fauces  to  the  pharynx;  the  second,  its  passage  through 
the  pharynx,  and  the  third  when  it  passes  through  the  oesophagus. 

In  the  first  stage,  the  tip,  body  and  base  of  the  tongue  press 
against  the  hard  palate,  and  push  the  bolus  along  toward  the 
pharynx,  the  teeth  being  closed.  The  palato-glossi  and  pharyngei 
then  contract  and  force  the  bolus  into  the  pharynx,  the  palatal 
curtain  being  carried  against  the  superior  pharyngeal  wall. 

In  the  second  stage  the  constrictors  contract,  the  epiglottis 
closes  the  top  of  the  larynx,  and  the  bolus  is  passed  into  the 
oesophagus. 

In  the  third  stage  the  oesophagus  contracts  on  the  bolus,  and 


1 84  EQUINE   PHYSIOLOGY. 

by  the  movement  of  its  circular  and  longitudinal  fibres  forces  it 
through  the  cardiac  orifice  of  the  stomach  into  that  viscus. 

The  first  stage  is  voluntary,  the  others  involuntary. 

The  horse  can  make  from  65  to  90  motions  of  deglutition  per 
minute  for  fluids. 

GASTRIC  DIGESTION. 

From  the  difficulty  or  impossibility  of  making  a  gastric  fistula 
in  the  horse,  the  amount  and  composition  of  the  gastric  juice  is 
hard  to  estimate.  Its  specific  gravity  is  about  10 10,  its  reaction 
acid  and  its  composition  is  as  follows — 


(  Water 

Fluids,  -j  Hydrochloric  acid \-    982.80 

(Lactic  acid 

Solids 17.20 


1 


1000.00 

The  solids  are — 

Pepsin, 

Milk-curdling  ferment, 

Chlorides, 

Phosphates, 

Iron. 

The  amount  of  acids  varies  from  0.084  per  cent,  to  0.2  per  cent. 

The  juice  from  the  fundus  of  the  stomach  contains  more  fer- 
ment, more  acid  and  more  mucus  than  that  from  the  pylorus. 
Action  of  Gastric  Juice. 

The  gastric  juice  changes  starch  into  sugar,  not  of  itself,  but  by 
the  saliva,  which  still  continues  its  action,  converts  vegetable 
albumin  into  peptones,  and  digests  cellulose  by  fermentation  to 
some  extent.  In  feeding  the  horse  the  food  should  be  taken  in 
the  following  order:  first  water,  second  hay,  third  oats,  as  the  water 
if  given  last  would  wash  the  food  into  the  intestine  before  it  was 
acted  upon  by  the  gastric  juice,  while  if  hay  was  given  after  oats, 
it  would  carry  them  along  with  it,  as  it  is  principally  digested  in  the 
intestines,  the  oats  being  acted  upon  by  the  stomach  for  the  most 
part.  The  stomach  is  never  completely  empty,  as  some  food 
remains  after  24  hours. 


ALIMENTATION. 


185 


Vomiting  in  the  horse  is  very  infrequent  and  difficult,  on  ac- 
count of  there  being  no  dilatation  of  the  stomach  at  the  point 
where  the  oesophagus  enters,  the  oesophagus  being  very  narrow  at 
its  termination  and  being  nearly  filled  by  folds  of  its  mucous  mem- 
brane. 

It  takes  place  by  a  deep  inspiration,  forcing  the  diaphragm  down 
and  fixing  it;  then  a  relaxation  of  the  oesophageal  orifice,  with  a 
spasmodic  contraction  of  the  abdominal  muscles,  completes  the 
act. 

THE  BILE. 

The  bile,  secreted  by  the  liver,  acts  upon  the  food  in  the  upper 
part  of  the  small  intestine.  It  is  brownish-green  in  color,  alkaline 
in  action,  bitter  in  taste.  Its  specific  gravity  is  higher  than  the 
gastric  and  lower  than  the  pancreatic  juice,  and  its  amount  in  24 
hours  is  from  11  to  13^  pounds. 

Its  composition  is  as  follows: — 

Water. 
Mucin. 


Bile  salts  /  Glycocholate  of  Soda, 
tf  lie  salts  1  Taurocholate  of  Soda- 

Bile  coloring  matter  {  j^j^. 


Cholesterin. 
Iron  and  salts. 

The  Mucin  comes  from  the  biliary  passages,  not  from  the  liver 
cells. 

Gmelin's  Test  for  Biliary  Pigment. 

Spread  a  drop  of  diluted  bile  on  a  porcelain  plate  and  add  a. 
drop  of  yellow  nitric  acid  to  it.     A  play  of  colors  results,  green, 
blue,  violet  and  yellow.     (Charles.) 

Pettenkofer's  Test  for  Biliary  Acids. 

Add  a  little  sugar  to  the  fluid,  then  shake  and  add  a  few  drops 
of  strong  sulphuric  acid.  A  beautiful  purple  or  violet  coloration 
will  appear. 

Cholesterin  is  excreted  by  the  liver,  and  is  derived  from  broken- 
down  nerve-tissue.  Under  the  microscope  it  appears  as  delicate, 
thin,  flattened,  super-imposed  plates,  with  one  corner  broken  off. 

13 


1 86  EQUINE   PHYSIOLOGY. 

Action  of  the  Bile  in  Digestion. 

i.  It  dissolves  and  emulsifies  fats  and  liberates  fatty  acids  in 
small  amounts. 

2.  It  acts  as  a  stimulus  to  peristalsis  by  its  irritant  action  on  the 
intestinal  mucous  membrane. 

3.  It  prevents  decomposition  of  faeces,  the  fasces  being  colored 
by  the  bile  pigments  in  the  form  of  hydro-bilirubin. 

4.  It  is  said  to  contain  a  ferment  in  small  amount,  capable  of 
converting  starch  into  sugar. 

Glycogenic  Function. 

From  observation  it  has  been  found  that  the  liver  has  another 
function — the  changing  of  the  carbohydrates  and  albumin  into  a 
new  substance,  glycogen,  C6H10O5,  whitish  in  color,  inodorous, 
amorphous,  insoluble  in  alcohol  or  ether,  but  imperfectly  soluble 
in  boiling  water  (Charles).  It  is  taken  up  in  the  form  of  glucose, 
then  stored  up  as  glycogen,  and  then  changed  into  glucose  again, 
when  it  is  carried  away  from  the  liver. 

Uses  oj  Glycogen. — It  is  probably  burned  up  in  the  lungs,  cir- 
culation and  muscles  in  generating  animal  heat,  and  in  muscular 
action. 

Puncture  of  the  floor  of  the  medulla  causes  glycosuria,  as  shown 
by  Bernard.  An  animal  deprived  of  bile  by  a  fistula  dies  of  star- 
vation after  losing  four-tenths  of  its  bodily  weight. 

THE  PANCREATIC  JUICE. 

The  secretion  of  the  pancreas  is  colorless  and  alkaline  in  reaction. 
It  is  coagulated  by  heat,  metallic  salts,  tannic  acid,  etc.;  is  easily 
decomposed,  emitting  an  offensive  odor.  Its  specific  gravity  is 
about  1020,  and  amount  in  24  hours  is  about  12 \  pounds.  Its 
composition  is  as  follows: — 

Water, 982.05 

Organic  matter,    8.88 

Ash, 8.59 

The  ash  consists  of  phosphates,  chlorides,  iron  and  magnesium. 

The  organic  matter  consists  of  four  ferments — an  amylolytic, 

a  proteolytic,  one  acting  on  fats,  and  a  milk-curdling  ferment. 

The  first  may  be  extracted  by  a  solution  of  arseniate  of  potas- 


ALIMENTATION.  187 

sium  with  a  little  ammonia  added;  the  second  by  potassium  iodide, 
and  the  third  by  a  solution  of  bicarbonate  of  soda  with  a  little 
caustic  soda. 

Action  of  the  Pancreatic  Juice. 

1.  It  changes  starch  and  glucose  into  sugar  rapidly  and  com- 
pletely.    Cane-sugar  not  acted  upon. 

2.  It  emulsifies  and  saponifies  fats  completely  with  the  aid  of 
the  bile. 

3.  It  converts  albumin  into  peptones. 

4.  It,  by  means  of  a  special  ferment,  curdles  milk.  This  fer- 
ment can  be  extracted  by  a  solution  of  common  salt,  but  has  not 
vet  been  isolated  in  the  horse. 

THE  INTESTINAL  JUICE. 

This  is  secreted  by  Brunner's  glands  and  the  crypts  of  Lieber- 
kuhn.  Its  specific  gravity  is  about  10 10,  alkaline  in  reaction, 
and  its  composition  is  as  follows  (Charles,  from  Colin): 

Water  98.10 

Solids 1 .90 

Albumin  and  other  organic  matters 0.45 

Carbonate  of  soda 1.45 

Its  amount  in  24  hours  is  difficult  to  estimate,  Colin  having 
found  about  12  ounces  an  hour  in  about  six  feet  of  gut.  This 
may  be  increased  by  injection  into  the  gut  of  irritants. 

Its  Action  is  much  the  same  as  the  pancreas,  dissolving  pro- 
teids  and  albumin,  and  converting  starch  into  sugar. 

The  gases  found  in  the  intestine  are  oxygen,  nitrogen,  carbon 
dioxide,  hydrogen,  ammonia,  carburetted  and  sulphuretted  hy- 
drogen. About  60  per  cent,  of  the  proteids  have  to  be  digested 
in  the  small  intestine. 

DIGESTION  IN  THE  LARGE  INTESTINE. 

The  Caecum  serves  as  a  reservoir  for  the  food  after  about  24 
hours,  the  fermentative  changes  of  the  small  intestine  still  going 
on  in  an  alkaline  medium.  About  20  per  cent,  of  the  food  is 
digested  in  that  viscus,  and  about  40  per  cent,  of  the  cellulose. 


1 88  EQUINE   PHYSIOLOGY. 

The  Colon  acts  principally  as  an  absorbing  area,  the  food  pass- 
ing through  its  several  curvatures  and  the  floating  colon  before 
reaching,  the  rectum.  The  diaphragmatic  curvature  contains 
large  amounts  of  fluid. 

THE  F^CES. 

The  residue  of  aliment  after  digestion  is  expelled  from  the  rectum 
in  rounded  balls  as  faeces.  Horses  defecate  every  three  hours, 
and  will  pass  about  17  kilos  or  37.4  pounds,  or  5.8  of  solids. 

About  13  per  cent,  are  inorganic  materials. 

DEFECATION. 

Defecation  is  the  process  of  evacuation  of  the  rectum.  The 
presence  of  fecal  matter  in  the  rectum  leads  to  the  desire  to  expel 
it.  The  brain  then  sends  an  inhibitory  action  to  the  reflex  centre 
in  the  lumbar  cord,  which  causes  a  relaxation  of  the  sphincter 
muscles.  Contraction  of  the  abdominal  muscles  and  small  colon, 
with  the  circular  fibres  of  the  rectum,  then  take  place,  causing  a 
propulsion  of  the  faeces  through  the  anus.  The  mucous  membrane 
of  the  opening  is  everted,  then  pulled  back  by  the  retractor  muscles. 

INTESTINAL  MOVEMENTS. 

The  food  is  carried  along  by  peristalsis,  a  worm-like  motion  of 
the  intestine  due  to  involuntary  contraction  of  both  the  longitudi- 
nal and  circular  muscular  fibres.  The  irritation  of  the  bile  is  an 
active  factor  in  keeping  it  up. 

ABSORPTION. 

Absorption  is  the  process  of  taking  up  the  food  principles  after 
digestion,  also  water  and  salts  that  have  not  been  acted  upon. 
It  takes  place  by  means  of  lymphatics  and  veins. 

By  veins. — The  water,  salts,  sugar,  soaps  and  peptones  are  ab- 
sorbed quickly  by  osmosis,  and  also  by  some  special  function  of 
the  epithelial  cells  of  the  villi. 

By  lymphatics. — This  takes  place  by  the  villi  (see  Intestines)) 
the  emulsified  food  elements  passing  into  their  interior  by  the 
intercellular  connective  tissue,  then  by  the  lymph  channels  of  the 


ABSORPTION.  189 

mesentery  to  the  receptaculum.  Lymph  is  an  alkaline,  viscid 
fluid  of  a  specific  gravity  of  about  1030;  its  amount  in  24  hours, 
72  kilos  or  158  pounds.  Its  composition  is  (Smith,  from  C. 
Schmidt) : 

Water, 963-93 

Solids, w 36.07 

1000.00 
Solids  are — 


i} 


Fibrin, 

Albumin,   ]■ 28.84 

Fats,  etc. 

Inorganic  salts 7.22 

36.06 


It  contains  lymph  corpuscles,  identical  with  white  blood  cor- 
puscles in  structure. 

The  course  of  the  lymph  is  from  the  various  lymphatics  of  the 
periphery  to  the  receptaculum,  then  through  the  thoracic  duct 
into  the  confluence  of  the  jugulars.  Chyle  is  lymph  during  diges- 
tion, and  contains  emulsified  fats  in  addition  to  its  usual  compo- 
sition. It  passes  through  the  villi  to  the  thoracic  duct.  Its  com- 
position (Charles,  from  Schmidt)  is — 

Serum, 96.74 

Clot, / 3-*5 

Water, 88.7 

Solids,  1 1.2 

Solids  are — 

Fats, 0.15 

Soaps, 0.03 

Fibrin, 3. 89 

Albumin,  sugar,  etc., 6.59 

Haematin,  salts 

After  a  meal  the  chyle  is  very  abundant,  during  fasting  very 
small  in  amount.  The  flow  of  lymph  is  kept  up  by  the  contrac- 
tion of  their  walls,  by  the  aspiration  of  the  diaphragm,  contraction 
of  the  abdominal  muscles,  and  the  peristalsis  of  the   intestines. 


190  EQUINE   PHYSIOLOGY. 


ANIMAL  HEAT. 


The  process  of  nutrition  and  oxidation  of  food  products  is  ac- 
companied by  the  evolution  of  heat.     This  gives  the  body  an 
average  temperature  which,  in  the  horse,  varies  between  37.50 
C.  and  380  C. 
Sources  of  Animal  Heat. 

This  is  the  result  of  oxidation  of  the  hydrocarbons  and  carbo- 
hydrates as  well  as  the  combination  of  hydrogen  and  oxygen  form- 
ing water. 

Heat  Units. — The  English  heat  unit  is  the  amount  of  heat  re- 
quisite to  raise  one  pound  of  water,  i°  F.  In  the  horse  for  each 
kilo  of  weight,  2.1  heat  units  are  set  free  per  hour,  or  for  an  ani- 
mal of  500  kilos,  as  an  example,  1050  heat  units  per  hour,  or  in  a 
day  2.1X500X24=25,200  heat  units.  In  a  man  of  140  pounds, 
13,440  heat  units  are  thrown  off  in  the  same  time. 

The  temperature  is  raised  by  exercise,  due  to  increased  tissue 
metabolism,  and  the  urea  is  increased. 

The  temperature  of  the  blood  of  the  portal  vein  is  usually  sev- 
eral degrees  higher  than  the  average  temperature  of  the  body. 

SECRETION. 

Secretion  (Flint)  is  the  act  by  which  fluids  holding  certain 
principles  in  solution  are  separated  from  the  blood,  or  are  manu- 
factured by  special  organs  from  materials  furnished  by  the  blood. 
These  have  a  function  to  perform. 

An  Excretion  contains  elements  not  formed  in  the  substance  of 
the  gland  which  have  no  function  to  perform  and  are  extracted 
from  the  blood. 

There  are  always  two  periods  in  every  secreting  organ — 

1st,  The  period  of  repose,  or  period  of  no  secretion;  though  the 
manufacture  of  the  solid  elements  is  constantly  going  on. 

2d,  The  period  of  junctional  activity,  in  which  the  formed  ele- 
ments are  washed  out  by  the  water  from  the  blood,  which  is  eight 
times  as  abundant  in  this  stage. 

Classes  of  secreting  organs. 

1.  The  most  simple  is  a  basement  membrane  covered  with  flat- 
tened cells,  as  the  peritoneum. 

2.  The  next  is  more  secreting  surface  with  not  much  more  space, 
as  the  simple  depressions  of  Lieberkuhn  in  the  small  intestines. 


ABSORPTION.  191 

3.  The  second  variety  have  two  or  more  branches  leading  into 
a  common  duct,  as  in  Brunner's  glands. 

4.  Where  a  number  of  the  third  variety  open  into  a  common 
duct,  the  compound  racemose  glands,  as  the  salivary  and  pan- 
creatic glands. 

5.  Tubular  glands  composed  of  a  number  of  elongated  tubes, 
as  in  the  testicle  and  kidney. 

6.  The  ductless  glands,  as  the  spleen  and  supra-renal  capsules. 

7.  Unclassified  glands,  as  the  liver. 

The  Permanent  fluids  are  the  aqueous  and  vitreous  humors  of  the 
eye,  synovial,  serous,  cerebrospinal  and  fluid  of  the  internal  ear. 

The  Transitory,  fluids  are  mucus,  cerumen,  sebaceous  matter, 
Meibomian,  tears,  milk  and  all  the  digestive  fluids. 

The  Excretions  are  the  urine,  sweat,  jozces,  and  bile,  which  is 
also  a  secretion  in  part. 

THE  PERSPIRATION. 

(For  anatomy  of  skin,  see  Sense  of  Touch.) 

The  perspiration  is  of  low  specific  gravity,  about  1004,  alkaline 
or  neutral  in  reaction,  and  contains  about  2  per  cent,  of  solids, 
consisting  of  urea,  fats,  cholesterin  and  salts.  Its  amount  varies 
with  exercise  and  in  different  parts  of  the  body,  being  most  abun- 
dant in  the  inguinal  region.  When  it  is  secreted  in  small  amounts 
not  to  be  seen  by  the  eye  it.  is  called  insensible;  when  in  large 
amounts,   sensible   perspiration. 

Its  junctions  are  the  regulation  of  animal  heat  and  also  excre- 
tion of  urea,  etc. 

Section  of  the  cervical  sympathetic  increases  the  secretion  in 
that  part,  and  certain  drugs,  as  Jaborandi,  have  a  like  action. 

The  Sabaceous  matter  of  the  skin  consists  of  about  J  water 
and  §  solids,  of  albumin,  epithelium,  fat,  soaps  and  salts. 

It  acts  as  a  lubricant  to  the  skin  and  hair. 

THE  MAMMARY  SECRETION. 

Milk  is  secreted  soon  after  the  birth  of  the  foal,  obtained  by 
suction,  is  alkaline  in  reaction  and  of  a  specific  gravity  of  about 
1030.     It  consists  of  (Charles,  from  Gorup-Besanez): 

Water  82.84 

Solids 17.16 


192  EQUINE    PHYSIOLOGY. 

Casein,      ")  , 

Albumin,  ] ^ 

Butter, 6.87 

Milk  sugar,       \                                                                            „  , 
Organic  salts,  /  5 

17.16 

The  gases  of  milk  (Pfliiger)  are  carbonic  anhydride,  oxygen 
and  nitrogen. 

Colostrum  is  the  milk  secreted  a  short  time  after  parturition.  It 
is  yellow  in  color,  of  a  higher  specific  gravity,  slightly  acid,  contains 
large  oil  globules  covered  with  casein,  and  has  purgative  properties. 

The  mammae  at  the  time  of  gestation  become  enlarged,  pend- 
ent, soft.  The  epithelium  becomes  rounded,  and  contains  a  large 
amount  of  fat. 

Milk  can  be  coagulated  by  acids,  tannin  and  mineral  salts  by 
coagulating  the  casein. 

Mare's  milk  contains  a  large  amount  of  sugar,  which,  by  the 
addition  of  an  acid  takes  on  a  lactic  acid  fermentation,  as  in  the 
preparation  of  koumiss. 

The  rapidity  and  amount  of  the  mammary  secretion  are  de- 
pendent on  arterial  pressure.  Certain  drugs  have  more  or  less 
action   upon   it. 

URINE. 

Urine,  the  excretion  of  the  kidneys,  is  a  watery,  yellowish  fluid, 
holding  in  suspension  many  solids,  which  are  excreted  in  this 
form.  It  is  alkaline  in  reaction  when  the  animal  feeds  on  vege- 
table food,  and  its  specific  gravity  varies  from  10 16  to  1060, 
usually  about  1050.  Its  composition  is  (Smith,  from  Boussin- 
gault): 

Urea : 31. 

Potass,  hippurate 4-7 

Alkaline  lactates 20. 1 

Potass,  bicarb 15.5 

Magn.  carb 4.2 

Calcium  carb *. 10.8 

Potass,  sulph 4.2 

Sodium  chloride o.  7 

Silica 1.0 

Water  910.0 

1 000.0 


ABSORPTION.  193 

Mucin  is  abundant.  The  urea  is  dependent  on  the  amount  of 
oats,  grain  and  roots  ingested,  the  hippuric  acid  (C9  Hg  N03),  to 
which  and  phenol  the  odor  is  due,  on  the  amount  of  green  stuff, 
hay  and  straw. 

The  amount  in  twenty-four  hours  is  five  or  six  litres,  varying 
with  the  amount  of  fluid  excreted  by  the  sweat  glands. 

The  secretion  of  urine  takes  place — 

1.  By  filtration,  the  water  and  soluble  salts  passing  out  into  the 
interior  of  the  glomerulus. 

2.  By  active  secretion,  urea  being  secreted  by  the  epithelial  cells 
of  the  convoluted  tubules.  The  latter  process  has  been  proved 
by  injecting  indigo  carmine  into  the  blood  after  section  of  the 
spinal  cord  to  prevent  filtration.  The  carmine  can  be  found  in 
the  cells  of  the  convoluted  tubes,  and  also  in  the  urine,  none 
being  found  in  the  glomerulus. 

Urine  is  decreased  in  summer,  due  to  the  increased  amount  of 
secretion  by  the  skin,  by  slowing  the  heart,  by  sleep  and  rest. 

It  is  increased  by  cold  weather,  stimulation  of  the  heart,  after 
eating,  and-  also  by  stimulation  of  the  medulla. 

After  secretion,  the  urine  passes  into  the  pelvis  of  the  kidney, 
through  the  ureter,  drop  by  drop,  into  the  bladder,  where  it  is 
accumulated  till  discharged,  the  bladder  being  emptied  three  or 
four  times  in  twenty-four  hours. 

Nervous  mechanism  of  micturition. 

The  centre  for  micturition  is  located  in  the  lumbar  enlargement 
of  the  cord.  The  sensation  of  fullness  is  carried  to  this  centre, 
which  sends  back  an  impulse,  relaxing  the  contracted  sphincter, 
and  causing  a  contraction  of  the  longitudinal  (or  detrusor)  fibres. 
This  forces  the  contents  into  the  urethra,  the  contraction  of  its 
fibres  terminating  the  act. 

After  section  of  the  spinal  cord,  a  condition  known  as  retention 
with  overflow  takes  place,  the  bladder  is  distended,  and  soon  also 
the  sphincter  vesica  by  mechanical  means,  the  urine  escaping 
drop  by  drop  and  soon  becoming  ammoniacal. 

THE  DUCTLESS  GLANDS. 

These  are  the  spleen,  see  Abdomen;  the  thyroid  and  thymus,  see 
Thorax;  and  the  supra-renal  capsules,  see  Kidney. 

The  Supra-renal  capsules  are  relatively  lareer  before  birth, 
can  be  extirpated  with  no  apparent  result,  are  probably  connected 


194  EQUINE   PHYSIOLOGY. 

in  some  way  with  the  sympathetic  system,  but  their  function  is 
not  known. 

The  Spleen  probably  influences  digestion,  and  Shiff  and  Herzon 
claim  that  the  secretion  of  trypsin,  one  of  the  pancreatic  ferments, 
is  dependent  on  it. 

In  its  structure  are  found  pigment,  broken-down  red  corpuscles 
and  many  leucocytes.  It  also  serves  as  a  reservoir  for  the  abdom- 
inal circulation.  It  can  be  removed  without  loss  of  life,  and 
is  a  blood  gland. 

The  Thyroid  and  Thymus  have  to  do  with  the  elaboration  of 
blood,  otherwise  their  function  is  unknown. 

The  Pituitary  Body  and  Conarium  also  properly  belong  in 
this  category,  but  their  function  is  unknown. 

THE  NERVOUS  SYSTEM. 

The  nervous  system  connects  into  a  coordinated  organism  all 
parts  of  the  body.  It  receives  all  impressions,  regulates  all 
movements,  voluntary  and  involuntary,  and  the  functions  of  secre- 
tion, nutrition,  calorification  and  all  processes  of  animal  life. 
(Flint.)  The  cerebrospinal  system  consists  of  the  brain,  cord  and 
the  various  nerves,  and  presides  over  animal  life.  The  sympa- 
thetic presides  over  nutrition  or  organic  life. 

(For  structure  of  nerves,  see  Anatomy  of  Nervous  System.) 

Termination  of  nerves. 

To  voluntary  muscular  fibres  the  nerve  divides  and  spreads  out 
into  plaques. 

To  involuntary  fibres,  it  loses  its  tubular  membrane  and  ter- 
minates in  the  nucleus  as  the  axis  cylinder. 

The  Sensory  nerves  terminate — 

(a)  As  minute  plexuses  with  no  fixed  arrangement. 

(b)  As  the  tactile  corpuscles  or  end  bulbs  of  Krause,  found  most 
abundantly  in  the  lip,  hoof,  sheath  and  glans  penis.  These  are 
small  capsules  of  connective  tissue,  the  nerve  terminating  in  a 
plexus  or  bulbous  extremity.  They  have  also  a  central  termination 
either  in  the  brain  or  cord,  connected  to  a  cell  pole  by  an  axis 
cylinder.  After  its  origin  a  nerve  does  not  inosculate  but  passes 
to  its  terminus. 

Nerves  are  divided  into  motor  and  sensory,  the  former  ending 


THE    NERVOUS    SYSTEM.  1 95 

in  muscles  and  conducting  the  stimulus  by  which  the  muscle  acts, 
the  latter  carrying  sensation  from  the  periphery  to  the  centre. 

Nerves  act  as  conductors,  but  do  not  produce  anything. 

A  nerve's  function  is  manifested  at  its  terminus. 

Nerve  stimulation  can  be  accomplished  mechanically,  chemi- 
cally or  thermically,  also  by  a  mild  current  of  electricity. 

Rate  of  nervous  conduction  is  250  feet  per  second  (electrotonus, 
for  lack  of  space,  will  not  be  described). 

The  Spinal  nerves  are  42  or  43  in  number,  arranged  in  pairs 
(for  description,  see  Nerves).  The  superior  or  sensory  nerves 
end  in  the  superior  or  sensory  horns  of  the  gray  matter  of  the 
cord,  the  inferior  or  motors  end  in  the  inferior  or  motor  horns. 
Stimulation  of  the  former  causes  pain  at  its  peripheral  distribution, 
and  section  loss  of  sensation  at  the  same  point.  Stimulation  of  the 
latter  causes  contraction  of  the  muscles  to  which  it  is  supplied, 
and  section  motor  paralysis  of  the  same. 

THE  CRANIAL  NERVES. 

The  First  or  Olfactory  will  be  discussed  under  Smell. 

The  Second  or  Optic  terminates  in  the  retina,  the  fibres  de- 
cussating. 

Section  of  one  tract  before  discussation,  causes  total  blindness 
of  the  outer  half  of  the  eye  of  the  same  side  and  the  inner  half  of 
the  opposite.  Injuries  of  the  visual  centre  produce  the  same 
result. 

The  Third  or  Oculo-motor  is  entirely  motor,  and  supplies  all 
the  muscles  of  the  eye,  except  the  external  rectus,  great  oblique 
and  part  of  the  posterior  rectus,  the  pupil  with  contractility  and 
movements  of  the  ciliary  muscles.  Section  causes  external  strabis- 
mus, ptosis,  dilation  of  the  pupil,  and  inability  to  rotate  the  globe 
in  a  vertical  direction. 

The  Fourth  or  Patheticus  is  entirely  motor,  and  paralysis 
causes  inability  to  rotate  the  eye  laterally. 

The  Fifth  or  Trifacial  is  a  mixed  nerve,  viz.,  both  sensory  and 
motor.  The  ophthalmic  and  superior  maxillary  branches  are 
entirely  sensory,  the  inferior  maxillary  both  sensory  and  motor. 
Division  of  the  nerve  in  front  of  the  Gasserian  ganglion  causes 
loss  of  sensation  in  its  course  and  also  trophic  changes  in  the  eye- 


196  EQUINE   PHYSIOLOGY. 

ball,  the  latter  not  taking  place  if  the  action  is  made  behind  the 
ganglion,  by  leaving  the  sympathetic  attachments  intact.  Stimu- 
lation causes  exquisite  pain,  as  it  is  the  most  sensitive  nerve  in 
the  body.  Section  of  the  inferior  maxillary  branch  causes  paral- 
ysis of  the  muscles  of  mastication  on  the  same  side,  and  loss  of 
sensation  in  one  lateral  half  of  the  tongue.  Stimulation  causes  a 
spasm  of  the-  same  muscles. 

The  Sixth  or  Abducens  is  purely  motor,  and,  if  cut,  we  have 
an  inability  to  carry  the  eye  outward. 

The  Seventh  or  Facial  is  motor,  and  also  sends  the  chorda 
tympani  as  a  special  nerve  of  taste  to  the  anterior  two-thirds  of 
the  tongue. 

Section  causes  paralysis  of  the  superficial  muscles  of  the  face, 
stapedius,  occipito-styloid,  digastric,  stylo-hyoid,  subcutaneous 
muscle  of  -the  neck  and  soft  palate  through  the  great  petrosal  to 
Meckel's  ganglion.  There  is  also  loss  of  taste  on  the  anterior 
two-thirds  of  the  tongue  on  the  same  side. 

Stimulation  causes  contraction  of  the  same  muscles. 

The  Eighth  or  Auditory  is  a  nerve  of  special  sense  purely. 
Section  produces  deafness  on  the  same  side. 

The  Ninth  or  Glosso-pharyngeal  is  a  mixed  nerve,  being 
one  of  general  sensation  to  the  pharynx  and  fauces,  of  special 
sense  of  taste  to  the  back  part  of  the  tongue,  and  of  motion  to 
the  pharyngeal  muscles  in  part.  It  is  concerned  obviously  in 
deglutition. 

The  Tenth  or  Pneumogastric. 

The  auricular  branch  gives  sensation  to  the  external  ear. 

The  pharyngeal  gives  sensation  to  pharynx  and  to  muscles  con- 
cerned in  deglutition. 

If  the  superior  laryngeal  branch  is  stimulated,  spasm  of  the 
glottis  and  diaphragm  results. 

If  the  inferior  laryngeal  is  cut,  an  arrest  of  the  respiratory 
movements  of  the  glottis  takes  place,  at  it  supplies  all  the  muscles 
of  the  larynx  except  the  crico-thyroid. 

Cardiac  Branches. — If  the  nerve  is  cut  in  the  neck,  its  inhibit- 
ory action  on  the  heart  is  taken  off  and  it  is  increased  in  fre- 
quency. Galvanization  of  the  peripheral  end  decreases  its  action 
and  stops  it  in  diastole,  if  strong  enough. 


THE   NERVOUS    SYSTEM.  1 97 

Pulmonary  Branches. — If  the  nerves  are  cut  in  the  neck,  the 
respirations  are  markedly  diminished,  death  finally  occurring. 
Galvanization  increases  the  number;  if  strong  may  arrest  it. 

(Esophageal  Branches. — Paralysis  of  these  causes  an  inability 
to  swallow  food,  which  remains  in  the  gullet.  It  is  finally  vomited 
by  irritation  of  the  tube. 

Gastric  Branches. — If  the  left  nerve  is  cut  during  digestion, 
secretion  and  motion  at  once  cease;  slightly  irritated,  it  causes 
glycosuria. 

After  division,  the  bile  becomes  more  fluid  in  character,  the 
formation  of  glycogen  ceases,  and  purgatives  have  no  longer  any 
effect. 
Eleventh  or  Spinal  Accessory. 

This  is  a  motor  nerve  as  well  as  supplying  the  larynx  through 
the  laryngeals. 

Stimulation  causes  spasm  of  the  sterno-maxillaris,  mastoido- 
humeralis,  and  cervical  and  dorsal  trapezius. 

Division  causes  paralysis  of  these  as  well  as  shortness  of  breath, 
from  incoordination  of  muscles  and  inability  to  make  a  prolonged 
vocal  sound. 
Twelfth  or  Hypoglossal. 

This  is  purely  motor  and  division  causes  paralysis  of  the  mus- 
cles of  the  tongue  and  difficulty  in  mastication  and  deglutition. 

THE  SPINAL  CORD. 

The  inferior  motor  roots  emerge  from  the  larger  extremity  of 
the  horn  of  gray  matter  on  either  side,  and  communicate  with  the 
large  multipolar  motor  cells  found  in  groups  in  that  situation. 

The  superior  or  sensory  roots  enter  the  cord,  immediately  com- 
municating with  the  tripolar  sensory  cells  of  the  smaller  extrem- 
ity of  the  gray  matter,  which  comes  to  the  surface. 

Some  of  both  the  motor  and  sensory  roots  enter  the  columns 
of  the  opposite  side  or  lateral  tracts,  not  all  of  the  fibres  thus  pass- 
ing up  or  down  at  the  same  point. 

Decussation  of  motor  and  sensory  tracts. 

Most  of  the  motor  nerves  cross  to  the  opposite  side  at  the  me- 
dulla, the  nerves  from  the  right  side  of  the  brain  ending  on  the 
left  side  of  the  body,  and  vice  versa.  Some  of  the  motor  roots 
continue  down  the  cord  on  the  same  side  as  the  direct  pyratnidal 
tract. 


198  EQUINE   PHYSIOLOGY. 

The  sensory  nerves  decussate  all  along  the  cord,  not  at  one  fixed 
point,  ending  at  the  sensory  portion  of  the  internal  capsule  and 
hippocampus  major.     Thus  one  side  of  the  brain  governs  the 
sensation  of  the  opposite  side. 
Functions  of  the  Cord. 

I.  As  a  conductor.     II.  As  an  independent  nerve  centre. 

I.  As  a  Conductor. — The  inferior  and  inferior  lateral  columns 
convey  motor  impulses  from  the  brain  to  the  periphery.  If  a  sec- 
tion of  both  motor  tracts  is  made,  motor  paralysis  will  result  below 
that  point.     If  one  tract,  motor  paralysis  on  the  same  side  only. 

If  the  sensory  portion  of  the  cord  is  cut  completely,  a  similar 
absence  of  sensation  below  that  point  and  inability  to  coordinate 
will  be  the  result.  If  a  unilateral  sensory  section  is  made,  there 
will  be  complete  loss  of  sensation  on  the  opposite  side. 

Section  of  one  lateral  half  of  the  cord  causes  motor  paralysis 
on  the  same  side,  with  hyperesthesia  and  sensory  paralysis  on  the 
other. 

II.  As  a  Nerve  Centre. — If  a  frog  is  decapitated  and  placed  in 
a  vacuum  it  will  remain  quiet.  Now,  if  its  surface  is  irritated,  mus- 
cular contraction  will  result.  If  the  cord  is  broken  up  no  such 
phenomena  take  place,  showing  that  the  cord  controlled  these 
movements,  which  are  called  reflex  actions.  The  sensory  nerves 
convey  the  impression  to  a  centre  in  the  cord,  which  sends  it 
back  to  the  muscles,  causing  a  contraction  (Flint). 

The  gray  substance  of  the  cord  is  neither  sensible  nor  excitable. 

The  inferior  lateral  white  columns  are  excitable  throughout,  but 
not  sensible. 

The  superior  columns  are  sensible,  more  so  at  the  entrance  of 
the  posterior  nerve-roots.  They  are  not  excitable.  Deeply,  they 
are  neither  excitable  nor  sensible. 

THE  ENCEPHALON. 

The  encephalon  consists  of  the  medulla  oblongata,  pons,  corpora 
striata,  corpora  quadrigemina,  optic  thalami,  olfactory  lobes,  cere- 
bellum and  cerebrum. 

MEDULLA   OBLONGATA. 

This  serves  as  a  medium  of  transmission  of  motor  and  sensory 
impulses,  and  also  as  the  centre  for  numerous  functions,  as  masti- 
cation, deglutition,  vomiting,  a  cardiac  centre,  a  vasomotor  centre 


THE   NERVOUS   SYSTEM.  1 99 

and  a  respiratory  centre.     The  glycosuric  centre  has  been  already 
referred  to  (see  Liver). 

PONS   VAROLII. 

The  superficial  fibres  are  not  excitable  or  sensible;  the  deeper 
are  excitable,  and  the  posterior  are  only  sensible.  It  presides  over 
voluntary  motion  and  sensation. 

CORPORA   STRIATA. 

Electrical  stimulation  of  one  of  these  causes  general  muscular 
contraction  on  the  opposite  side.  Destruction  of  the  internal  cap- 
sule causes  loss  of  motion  and  sensation  on  the  opposite  side  of 
the  body.  The  anterior  part  of  the  internal  capsule  is  motor, 
the  posterior  sensory. 

CORPORA   QUADRIGEMINA. 

They  are  situated  in  the  path  of  visual  conduction,  and  are  con- 
nected with  the  sense  of  sight  and  the  reflex  movement  of  the  iris. 

OPTIC  THALAMI. 

These  are  probably  connected  with  sensation,  vision  and  com- 
plex muscular  actions,  though  their  function  is  not  thoroughly 
understood. 

OLFACTORY   LOBES. 

These  are  the  centres  for  the  special  sense  of  smell,  and  their 
destruction  causes  a  loss  of  this. sense.  Fibres  have  been  traced 
to  the  uncinate  gyrus,  temporo-sphenoidal  region  and  optic 
thalami. 

CEREBELLUM. 

The  cerebellum  presides  over  the  coordination  of  movements 
of  progression,  being  connected  intimately  with  the  superior  col- 
umn of  the  cord.  Their  destruction  leads  to  absence  of  coordi- 
nation. 

CEREBRUM. 

The  cerebral  hemispheres  are  the  centres  of  intellect  or  .mind, 
receiving  impressions  and  giving  off  impulses.  An  animal  de- 
prived of  the  cerebrum  retains  the  special  senses  of  sight,  sound, 
taste,  etc.,  but  the  intellectual  faculties  are  all  lost.  From  experi- 
mentation on  the  lower  animals  and  by  observation  in  disease, 
centres  have  been  located  which  preside  over  certain  functions. 

The  motor  area  is  located  in  the  cortex  above  the  fissure  of 


200  EQUINE   PHYSIOLOGY. 

Sylvius  and  at  the  junction  of  the  anterior  with  the  middle  third 
of  the  surface.  The  upper  part  presides  over  the  hinder  extrem- 
ity of  the  opposite  side,  the  middle  over  the  anterior  extremity, 
and  the  lower  over  the  face.  In  front  of  the  latter  in  man  is 
found  the  speech  centre  on  the  left  side. 

The  centre  for  sight  is  located  in  the  occipital  region;  those  for 
smell,  hearing  and  taste  in  the  temporo-sphenoidal  region. 

THE  SYMPATHETIC  SYSTEM. 

This  chain  of  twenty-eight  ganglia  is  sensible  after  long  stimu- 
lation. 

After  section  of  the  cord  in  the  neck,  there  is  increased  vascu- 
larity by  paralyzing  the  coats  of  the  small  vessels. 

Functions. — It  influences  the  general  process  of  nutrition  and 
forms  the  vasomotor  system.  This  sends  branches  to  small  blood- 
vessels, and  influences  local  circulation  by  vaso-dilators  and  vaso- 
contr  actors. 

SPECIAL  SENSES. 

TOUCH. 

When  a  foreign  body  is  brought  into  contact  with  the  surface, 
it  is  appreciated  by  the  nerves  of  the  part  as  the  special  sense  of 
touch. 

This  sense  is  located  in  the  skin  and  also  on  mucous  membranes 
for  a  certain  distance.  The  termination  of  nerves  in  the  skin  has 
been  already  noticed.  In  the  horse,  with  a  single  digit  covered 
with  hard  material,  the  hoof  is  an  imperfect  organ  of  touch,  but 
can  estimate  solidity  and  resistance. 

The  lip  is  a  well-marked  tactile  organ,  the  end  bulbs  of  Krause 
being  very  abundant. 

SMELL. 

The  sense  of  smell  is  very  acute  in  the  horse.  It  has  already 
been   sufficiently  considered  under  the   anatomical   description. 

taste. 
Taste  enables  the  animal  to  detect  the  flavor  of  substances. 
The  anterior  two-thirds  of  the  tongue  preside  over  the  ability  to 
recognize  acids  and  alkalies,  and  is  supplied  by  the  chorda  tym- 


SPECIAL   SENSES.  201 

pani  of  the  seventh,  the  posterior  one-third,  recognizing  bitters 
and  sweets,  being  supplied  by  the  glosso-pharyngeal  nerve.  The 
circumvallate  or  calyciform  papillae  are  probably  gustatory,  the 
other  papillae  serving  to  entangle  substances,  so  that  their  flavor 
can  be  detected. 

HEARING. 

The  External  Ear  collects  the  sound-waves  and  carries  them 
inward  to  the  membrana  tympani. 

The  Middle  Ear. 

The  membrana  tympani  receives  the  sound-waves  and  transmits 
them  through  the  ossicles  to  the  foramen  ovale  opening  into  the 
vestibule. 

The  Eustachian  tube  allows  air  to  enter  the  tympanum,  and 
thus  equalizes  the  pressure  on  both  sides  of  the  membrana  tympani. 
The  guttural  pouch,  at  its  termination  below,  is  probably  connec- 
ted with  phonation. 

The  Internal  Ear. 

The  semicircular  canals  have  some  function  connected  with 
maintaining  equilibrium. 

The  organs  of  Corti  are  probably  the  essential  parts  of  the  in- 
ternal ear,  and  here  the  sound-waves  are  recognized,  each  sound 
by  a  separate  organ,  the  organs  receiving  the  waves  by  vibrations 
of  the  endolymph  transmitted  from  the  perilymph. 

SIGHT. 

Sight  is  the  special  sense  by  which  we  are  enabled  to  form  an 
idea  of  objects  by  means  of  the  eye. 

Mechanism. 

The  rays  of  light  enter  the  eye  by  passing  through  the  cornea, 
aqueous  humor,  pupil,  crystalline  lens  and  vitreous  to  the  retina, 
where  they  are  recognized  and  the  impression  sent  to  the  brain 
by  the  optic  nerve. 

The  junction  of  the  cornea,  aqueous,  and  lens  is  to  refract  the 
rays  of  light  and  bring  them  to  a  focus  on  the  retina. 

The  iris  regulates  the  amount  of  light  entering  the  eye  by 
means  of  its  muscular  fibres  dilating  and  contracting  the  pupil. 

The  retina  receives  the  impression  of  light,  the  layer  of  rods 

14 


202  EQUINE   PHYSIOLOGY. 

and  cones  being  the  most  sensitive  portion.     The  point  of  en- 
trance of  the  optic  nerve  is  known  as  the  blind  spot. 

Accommodation. 

When  an  object  is  distant,  the  rays  of  light  are  more  parallel, 
less  refraction  is  necessary,  and  the  lens  is  flattened.  When  the 
object  is  near,  the  opposite  condition  holds,  the  lens  becoming 
convex  by  contraction  of  the  ciliary  muscle;  this  decreasing  the 
intra-ocular  pressure  and  allowing  the  lens  to  increase  in  thick- 
ness. In  the  ordinary  condition  the  intra-ocular  pressure  on  the 
suspensory  ligament  of  the  lens  retains  it  in  a  flattened  state. 

Space  need  not,  obviously,  be  given  to  errors  of  refraction  and 
accommodation. 

.REPRODUCTION. 

For  discussion  of  copulation  and  development  of  the  embryo, 
see  works  on  Veterinary  Obstetrics  and  Embryology. 


COMPLIMENTS 
OF 


P.  Mask's  Son  Co, 

in,  Pi 


INDEX. 


Abdomen,  123 
Absorption,  188 
Anatomy,  9 
Angeiology,  81 
Animal  heat,  190 
Anus,  128 
Aorta,  anterior,  8s 

common,  85 

posterior,  93 

thoracic,  93 
Arterial  pressure,  176 
Arteries,  structure  of,  85 
Artery,  anterior  radial,  87 
tibial,  97 

axillary,  85 

collateral  of  cannon,  88 

common  carotid,  89 
interosseous,  88 

external  carotid.  91 
iliac,  96 

femoral,  96 

humeral,  87 

internal  carotid,  91 
iliac,  96 

pedal,  98 

popliteal,  97 

posterior  radial,  87 
tibial,  97 

pulmonary,  98 

spermatic,  95 
Arthrology,  37 
Articulations,  37 

of  anterior  extremity,  41 

classes  of,  37 

hyoid,  40 

of  lower  jaw,  39 

of  posterior  extremity,  45 

structure  of,  38 

thoracic,  40 

vertebral,  38 


Bile,  action  of,  186 
amount  of,  185 
composition  of,  185 
tests  for,  185 

Bladder,  144 

Blood,  amount  of,  173 
coagulation  of,  174 
composition  of,  173 
gases  in  arterial,  179 

venous,  179 
plasma  of,  173 


Bone,  hyoid,  24 

number  of,  10 

structure  of,  10 
Bones  of  anterior  extremity,  25 

face,  18 

head, 13 

pelvis,  31 

posterior  extremity,  31 

thorax,  24 

varieties  of,  9 

vertebral  column,  11 
Brain  (see  Cerebrum) 

membranes  of,  105 
Bronchi,  138 


Caecum,  128 

digestion  in,  187 
Cerebellum,  107 

function  of,  199 
Cerebrum,  105 

fissures  of,  107 

functions  of,  199 

lobes  of,  108 

ventricles  of,  109 
Chyle,  composition  of,  189 
Circulation,  175 

nervous  mechanism  of,  177 
Colon,  large,  128 

small,  128 
Concha,  157 
Corpora  quadrigemina,  106 

function  of,  199 
Cowper's  glands,  148 


Pefecation,  188 

nervous  mechanism  of,  i? 
Deglutition,  183 

stages  of,  183 
Digestion,  180 

in  large  intestine,  187 
Digestive  system,  120 
Ductless  glands,  140 

function  of,  193 
Duodenum,  125 


Ear,  157 

external,  157 
canal  of,  159 
cartilages  of,  157 
muscles  of,  158 


(203) 


204 


INDEX. 


Ear,  internal,  161 

middle,  159 
Epididymis,  146 
Eustachian  tube,  160 
Excretion,  190 
Expiration,  178 

changes  of  air  in,  178 

muscles  of,  178 
Eye,  appendages  of,  166 

blood  supply  of,  167 

function  of,  201 

humors,  162 

muscles  of  globe  of,  165 
lids  of,  165 

tunics  of,  162 


F.-eces,  188 

amount  of,  188 
Fluids,  permanent,  191 

transitory,  191 
Food,  181 

amount  of,  required,  181 

Gastric  juice,  action  of,  184 
amount  of,  184 
composition  of,  184 

Guttural  pouches,  160 

Hair,  168 

Hearing,  201 

Heart,  blood  supply  of,  84 

cavities  of,  83 

diastole  of,  17s 

nerve  supply  of,  84 

number  of  pulsations  of,  176 

sounds  of,  175 

systole  of,  175 

valves  of,  83,  84 

weight  of,  81 
Heat  units,  number  of,  190 
Hoofs,  168 
Hymen,  151 

Ileum,  125 

Inspiration,  muscles  of,  177 
Intestinal  juice,  action  of,  186 
composition  of,  187 
movements,  188 
Isthmus,  parts  of,  106 

Jeiunum,  125 

Kidneys,  141 

function  of,  192 
hilum  of,  141 

Malpighian  bodies  of,  141 
pelvis  of,  141 


irynx,  133 
cartilages  of,  133 
ligaments  of,  134 
movements  of,  177 
muscles  of,  135 
nerve  supply  of,  136 


Liver,  129 

fissures  of,  129 

glycogenic  functions  of,  186 

ligaments  of,  129 

lobes  of,  129 

parenchyma  of,  129 
Lungs,  138 
Lymph,  amount  of,  189 

composition  of,  189 
Lymphatic  duct,  103 

glands,  102 
Lymphatics,  102 

Malpighian  corpuscles,  143 
Mammary  glands,  155 

function  of,  191 
Mastication,  182 
Mastoid  cells,  159 
Mediastinal,  140 
Medulla  oblongata,  105 

function  of,  198 
Membrana  tympani,  159 
Micturition,  mechanism  of,  193 
Milk,  composition  of,  191 
Mouth,  120 
Muscles,  appendages  of,  50 

of  abdomen,  65 

of  anterior  extremity,  66 

of  back, 63 

of  ear,  158 

of  eye,  165 

of  face, si 

of  foot,  72 

of  hyoid,  54 

of  inferior  cervical  region,  57 

of  leg,  77 

of  mastication,  53 

of  palate,  55 

of  pelvis,  72 

of  perineum,  150 

of  pharynx,  56 

of  tail,  80 

of  thigh, 75 

of  thorax, 63 

of  tongue,  55 

of  trunk,  57 

structure  of,  50 

varieties  of,  50 
Myology,  50 

Nasal  fossae,  155 
Nerve,  abducens,  113    . 

auditory,  113 

facial,  113 

glossopharyngeal,- 1 13 

hypo-glossal,  114 

oculo-motor,  in 

olfactory,  m 

optic,  in 

patheticus,  in 

pneumogastric,  114 

spinal  accessory,  114 

tri-facial,  112 

ganglia  of,  m 
Nerves,  brachial  plexus  of,  115 

cervical,  115 


INDEX. 


205 


Nerves,  cranial,  function  of,  195 

dorsal,  118 

lumbo-sacral  plexus  of,  117 

structure  of,  103 

terminations  of ,  103 
Nervous  system,  103 

divisions  of,  103 
structure  of,  103 
Neurology,  103 
Nostrils,  156 

(Esophagus,  122 

Olfactory  lobes,  function  of,  199 

Optic  thalami,  107 

Orbits,  162 

Ossicles  of  tympanum,  160 

Ovaries,  153 

Oviducts,  153 

Palate,  120 
Pancreas,  131 

Pancreatic  juice,  action  of,  186 
amount  of,  186 
composition  of,  186 
Pericardium,  81 
Perineum,  150 
Peritoneum,  132 

reflections  of,  133 

structure  of,  133 
Penis,  149 
Perspiration,  191 

function  of,  191 
Peyer's  glands,  127 
Pharynx,  122 
Physiology,  173 
Pineal  gland,  107 
Pituitary  gland,  107 
Pleura,  139 
Pons  varolii,  106 

function  of,  199 
Prehension,  181 
Prostate  gland,  148 

Receptaculum  chyli,  103 

Rectum,  128 

Reflex  action,  198 

Reproduction,  202 

Respiration,  177 

nervous  mechanism  of,  179 
number  of  movements  of,  178 

Respiratory  organs,  133 

Saliva,  183 

amount  of,  183 

composition  of,  183 

function  of,  183 
Salivary  glands,  122 

structure  of,  122 

varieties  of,  122 
Schneiderian  membrane,  156 
Secretion,  190 
Sight,  201 

Sinuses  of  dura,  99 
Skin,  167 

glands  of,  168 


Skull,  fossae  of,  23 
Small  intestine,  125 
Smell,  200 
Spinal  cord,  103 

columns  of,  104 
fissures  of,  104 
functions  of,  198 
membranes  of,  104 
Spleen,  132 

function  of,  194 
Stomach,  123 

capacity  of,  123 
coats  of,  123 
glands  of,  125 
Supra-renal  capsules,  144 

function  of,  193 
Sympathetic  nervous  system,  118 
function  of,  193 

Taste,  nerves  of,  157 

papillae  of,  157 
Teeth,  120 

action  of,  182 

structure  of,  121 

varieties  of,  121 
Testicles,  145 

descent  of,  146 

function  of,  147 
Thoracic  duct,  103 
Thorax,  140 
Thymus,  141 

function  of,  194 
Thyroid,  140 

function  of,  194 
Tongue,  120 
Touch,  200 
Trachea,  136 
Tunica  vaginalis  testis,  14s 

Ureters,  144 
Urethra,  female,  151 

male,  148 
Urinary  organs,  141 
Urine,  192 

composition  of,  192 
Uriniferous  tubes,  143 
Uterus,  152 

Vagina,  151 
Valve,  pyloric,  124 

of  Vieussens,  no 
Valvulae  conniventes,  127 
Vas  deferens,  147 
Veins,  jugular,  99 

of  abdomen,  101 

of  anterior  extremity,  99 

of  head  and  neck,  99 

of  posterior  extremity,  102 

portal,  101 

pulmonary,  102 

saphenous,  102 
Vesiculse  seminales,  147 
Villi,  127 
Viscera,  120 
Vulva,  150 

bulbs  of,  151 


cA    Companion    Volume    to    Goutcfs    docket    ^Dictionary 

A  POCKET  CYCLOPEDIA 


OF 


MEDICINE  *  SVRGERY 


EDITED  BY 

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